Tryptophan
13 benefits mapped to clinical evidence across supplements.
Dose per serving from products
742 products in our catalogue print how much Tryptophan a serving holds.
Most common: 250 mg to 500 mg, 39% of 742 products.
| Dose per serving | Products |
|---|---|
| 10 mg or less | 22 |
| 10 mg to 25 mg | 21 |
| 25 mg to 50 mg | 36 |
| 50 mg to 100 mg | 99 |
| 100 mg to 250 mg | 116 |
| 250 mg to 500 mg | 291 |
| 500 mg to 1 g | 122 |
| over 1 g | 35 |
Dose per serving from research
63 study groups in 43 studies say how much Tryptophan participants took a day.
These are the doses the studies gave. They are not a recommendation.
Most common: 2.5 g to 5 g, 22% of 63 study groups.
| Daily dose | Study groups |
|---|---|
| 100 mg or less | 3 |
| 100 mg to 250 mg | 7 |
| 250 mg to 500 mg | 7 |
| 500 mg to 1 g | 11 |
| 1 g to 2.5 g | 13 |
| 2.5 g to 5 g | 14 |
| 5 g to 10 g | 7 |
| over 10 g | 1 |
Commonly used together
24 of 68 study groups took Tryptophan with something else. Shown: what 3 or more different studies gave.
What was given together, not what works together.
| Taken with | Study groups |
|---|---|
| Essential Amino Acids | 12 |
| L-Tyrosine | 4 |
| Glycine | 3 |
Benefit Evidence
Stress resilience: ↓ cortisol/anxiety
Stress resilience: ↑ mood/sleep
↑ satiety hormones; ↓ intake
Trp/LNAA shifts; appetite changes
5-HTP/Trp ↓ hunger
Sleep ↑, anxiety ↓
Tryptophan depletion worsens anxiety
Mood/stress changes, sleep ↑
Sleep/Fatigue: better sleep, less fatigue
Performance: faster recovery, energy
↑ satiety hormones; ↓ intake
Trp/LNAA shifts; appetite changes
5-HTP/Trp ↓ hunger
Sleep ↑, anxiety ↓
Tryptophan depletion worsens anxiety
Mood/stress changes, sleep ↑
Sleep/Fatigue: better sleep, less fatigue
Performance: faster recovery, energy
Research sources
Mood balance (64)
- [Effect of acupuncture-moxibustion on negative emotions and plasma tryptophan metabolism in patients with Crohn's disease at active stage]
PubMed ID: 33559436
Acupuncture+moxibustion reduced anxiety/depression in Crohn’s with concurrent Trp–Kyn pathway changes (clinical mood improvement).
- Tryptophan-depletion challenge in depressed patients treated with desipramine or fluoxetine: implications for the role of serotonin in the mechanism of antidepressant action
PubMed ID: 10418696
TRP depletion reversed SSRI (fluoxetine) response in many patients, strongly linking TRP/serotonin to antidepressant efficacy.
- Effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reaction in patients with post-stroke depression
PubMed ID: 39112627
Phototherapy increased plasma tryptophan and significantly improved depressive symptoms in post‑stroke depression RCT.
- Effect of Talbinah food consumption on depressive symptoms among elderly individuals in long term care facilities, randomized clinical trial
PubMed ID: 23493965
Talbinah (high Trp ratio food) produced large short‑term reductions in depressive symptoms in elderly residents.
- Effects of Branched-Chain Amino Acids on Skeletal Muscle, Glycemic Control, and Neuropsychological Performance in Elderly Persons with Type 2 Diabetes Mellitus: An Exploratory Randomized Controlled Trial
PubMed ID: 36235570
BCAA vs soy increased serum tryptophan and improved depressive symptoms in elderly T2D (mood signal).
- Metabolome-associated psychological comorbidities improvement in irritable bowel syndrome patients receiving a probiotic
PubMed ID: 38717445
B. longum NCC3001 increased circulating TRP and correlated with reduced amygdala reactivity and improved depression/anxiety scores (imaging+clinical link).
- Effects of acute treatment with a tryptophan-rich protein hydrolysate on plasma amino acids, mood and emotional functioning in older women
PubMed ID: 24858376
Acute Trp‑rich protein hydrolysate raised TRP availability and modestly improved mood/wellbeing and reduced fatigue.
- Recognizing emotions in faces: effects of acute tryptophan depletion and bright light
PubMed ID: 19939873
ATD impaired facial emotion recognition in dim light, implying normal TRP supports social cue processing and social ease.
- Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders
PubMed ID: 8080345
Acute TRP depletion caused large plasma Trp fall and clinically meaningful mood drops in at‑risk men—strong link between Trp availability and mood.
- The neurobiology of tryptophan depletion in depression: effects of intravenous tryptophan infusion
PubMed ID: 9513749
IV TRP after depletion tended to reduce depressive symptoms (trend).
- A placebo-controlled clinical trial of L-tryptophan in premenstrual dysphoria
PubMed ID: 10023508
Randomized trial: L-tryptophan reduced luteal-phase mood symptoms in premenstrual dysphoria.
- A placebo-controlled study of the effects of L-tryptophan in patients with premenstrual dysphoria
PubMed ID: 10721042
Replication of L-tryptophan benefit for premenstrual mood symptoms.
- Preliminary randomized double-blind placebo-controlled trial of tryptophan combined with fluoxetine to treat major depressive disorder: antidepressant and hypnotic effects
PubMed ID: 11022398
Tryptophan augmentation of fluoxetine produced faster early antidepressant effects (significant early HDRS improvement).
- The effect of tryptophan on social interaction in everyday life: a placebo-controlled study
PubMed ID: 11425511
Oral tryptophan changed everyday social behavior in healthy volunteers: less quarrelsome and more dominant (robust placebo‑controlled crossover with behavioral endpoints).
- Clinical and neurochemical effect of acute tryptophan depletion in unaffected relatives of patients with bipolar affective disorder
PubMed ID: 11513817
Unaffected relatives of bipolar patients showed mood lowering after depletion, suggesting tryptophan supports mood stability in vulnerable individuals.
- Baseline prolactin and L-tryptophan availability predict response to antidepressant treatment in major depression
PubMed ID: 12439628
Baseline TRP availability predicted antidepressant outcome interactions — clinical link with emotional recovery.
- Association between serotonin transporter gene promoter polymorphism (5HTTLPR) and behavioral responses to tryptophan depletion in healthy women with and without family history of depression
PubMed ID: 12090814
TRP depletion produced genotype‑dependent increases in depressive symptoms (s/s 5‑HTTLPR) — solid evidence TRP affects mood vulnerability.
- Neural and behavioral responses to tryptophan depletion in unmedicated patients with remitted major depressive disorder and controls
PubMed ID: 15289275
Tryptophan depletion induced transient relapse of depressive symptoms in remitted MDD, providing strong evidence that TRP availability supports mood stability.
- Cognitive therapy does not prevent a response to tryptophan depletion in patients also treated with antidepressants
PubMed ID: 16039618
ATD robustly reduced plasma Trp in remitted depressed patients; mood response was not altered by cognitive therapy, showing complex but relevant Trp–mood interactions.
- Reversed diurnal variation in depression: associations with a differential antidepressant response, tryptophan: large neutral amino acid ratio and serotonin transporter polymorphisms
PubMed ID: 15856721
Observational link between higher TRP:LNAA and poorer SSRI response in a depression subtype — associative evidence tying Trp availability to depressive symptom patterns.
- Tryptophan supplementation induces a positive bias in the processing of emotional material in healthy female volunteers
PubMed ID: 16767422
Two‑week Trp shifted emotional processing towards positive and reduced vigilance to negative cues in women — strong evidence for emotional balance.
- Effect of tryptophan depletion on smokers and nonsmokers with and without history of major depression
PubMed ID: 16893526
ATD triggered stronger depressive symptoms in individuals with past recurrent depression, showing Trp availability causally affects mood in vulnerable people.
- Differential effects of 5-HTTLPR genotypes on the behavioral and neural responses to tryptophan depletion in patients with major depression and controls
PubMed ID: 16953000
Tryptophan depletion changed mood-related behavior with genotype-dependent limbic metabolic changes, indicating Trp modulates mood circuits.
- Interactive effects of sex and 5-HTTLPR on mood and impulsivity during tryptophan depletion in healthy people
PubMed ID: 17544379
Acute ATD caused sex‑ and genotype‑dependent mood reductions (women) and behavioral changes — supports mood sensitivity to Trp.
- Effects of carbohydrates on brain tryptophan availability and stress performance
PubMed ID: 17689173
Carbohydrate-induced increase in Trp:LNAA was associated with improved mood and performance during experimental stress.
- Plasma NPY concentrations during tryptophan and sham depletion in medication-free patients with remitted depression
PubMed ID: 18281099
Tryptophan depletion transiently raised depression ratings in remitted depressed patients, implying tryptophan supports mood stability.
- Acute tryptophan depletion and self-injurious behavior in aggressive patients and healthy volunteers
PubMed ID: 18946662
Lowering TRP increased self-aggressive choices, pointing to TRP's role in regulating aversive emotional/behavioral responses.
- Differential effects of 5-HTTLPR genotypes on mood, memory, and attention bias following acute tryptophan depletion and stress exposure
PubMed ID: 19083208
ATD lowered mood in all subjects and produced larger effects in short-allele 5-HTTLPR carriers, supporting TRP role in mood vulnerability.
- Serotonin transporter genotype and depressive phenotype determination by discriminant analysis of glucose metabolism under acute tryptophan depletion
PubMed ID: 18718871
ATD provoked depressive relapse in remitted MDD subjects — strong evidence that TRP/serotonin supports mood maintenance.
- Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress
PubMed ID: 18551283
ATD reduced responsiveness to positive words under stress (affective processing), especially in at-risk individuals.
- The effects of tryptophan depletion on neural responses to emotional words in remitted depression
PubMed ID: 19539268
ATD altered habenula/amygdala blood flow correlated with negative bias—direct neural evidence for emotional regulation by TRP.
- Impact of acute tryptophan depletion on mood and eating-related urges in bulimic and nonbulimic women
PubMed ID: 19721848
ATD lowered mood across women and increased binge urges in medicated bulimics — implicates TRP in mood regulation.
- The effects of acute tryptophan depletion on mood in patients with Parkinson's disease and the healthy elderly
PubMed ID: 19625388
Acute tryptophan depletion caused a small but significant worsening in depressive symptoms in elderly and Parkinson patients (inverse evidence).
- The short (S) allele of the serotonin transporter polymorphism and acute tryptophan depletion both increase impulsivity in men
PubMed ID: 20188795
ATD increased impulsive responding (men) and produced behavioral changes; by inference restoring tryptophan availability could reduce such negative behavioral traits linked to mood regulation.
- An fMRI study on the role of serotonin in reactive aggression
PubMed ID: 22110714
ATD reduced reactive aggression in low‑trait‑aggressive subjects (modulates aggressive/irritable behavior).
- Food can lift mood by affecting mood-regulating neurocircuits via a serotonergic mechanism
PubMed ID: 24076224
Single Trp‑enriched drink raised plasma TRP/LNAA and produced acute subjective mood improvement with fMRI changes in mood circuits.
- The effects of vagus nerve stimulation on tryptophan metabolites in children with intractable epilepsy
PubMed ID: 25022821
Vagus nerve stimulation increased an endogenous Trp metabolite (anthranilic acid) correlated with mood improvement—indirect support.
- Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women
PubMed ID: 25572038
Randomized trial of a low‑dose bioavailable TRP product shifted emotional bias away from negative stimuli and increased subjective energy—direct positive effect on mood/emotional processing.
- Empathic accuracy and oxytocin after tryptophan depletion in adults at risk for depression
PubMed ID: 26462806
ATD reduced positive affect and lowered oxytocin in a subset, indicating Trp affects positive emotional states and social‑emotional hormones.
- Intake of tryptophan-enriched whey protein acutely enhances recall of positive loaded words in patients with multiple sclerosis
PubMed ID: 28153503
Tryptophan-enriched whey acutely raised plasma TRP and enhanced recall of positive words (affective memory), consistent with mood benefit.
- Acute tryptophan loading decreases functional connectivity between the default mode network and emotion-related brain regions
PubMed ID: 30585373
Acute tryptophan loading altered connectivity between DMN and emotion‑related regions — supports improved emotion regulation mechanistically.
- Effect of Tryptophan, Vitamin B(6), and Nicotinamide-Containing Supplement Loading between Meals on Mood and Autonomic Nervous System Activity in Young Adults with Subclinical Depression: A Randomized, Double-Blind, and Placebo-Controlled Study
PubMed ID: 31902864
7‑day low‑dose tryptophan + B6/nicotinamide improved depressive mood scores in young adults with subclinical depression (direct clinical effect).
- Bifidobacterium breve CCFM1025 attenuates major depression disorder via regulating gut microbiome and tryptophan metabolism: A randomized clinical trial
PubMed ID: 34875345
RCT probiotic modulated gut Trp metabolism and produced significant reductions in depressive scores—strong mood signal linked to Trp pathways.
- Tryptophan-enriched diet or 5-hydroxytryptophan supplementation given in a randomized controlled trial impacts social cognition on a neural and behavioral level
PubMed ID: 34737364
Trp interventions (5‑HTP and TRP-enriched diet) altered moral judgement and improved emotion-recognition and relevant brain activity—strong link to social cognition and ease.
- SLC6A4 polymorphisms modulate the efficacy of a tryptophan-enriched diet on age-related depression and social cognition
PubMed ID: 33743283
A tryptophan‑enriched diet improved age‑related depressive symptoms (and raised urinary 5‑HIAA) in S'S' SLC6A4 genotype carriers — direct dietary evidence for mood benefit in a defined subgroup.
- Serotonin depletion amplifies distinct human social emotions as a function of individual differences in personality
PubMed ID: 33518708
ATD increased negative social emotions (guilt/annoyance) and trait‑dependent social reactions—indicates Trp availability modulates social emotionality (inverse implication).
- Acute tryptophan depletion balances altered resting-state functional connectivity of the salience network in female patients recovered from anorexia nervosa
PubMed ID: 36195339
TRP depletion normalized abnormal salience‑network connectivity in recovered anorexia (effect on emotion‑related circuits).
- Decreased Gut Microbiome Tryptophan Metabolism and Serotonergic Signaling in Patients With Persistent Mental Health and Gastrointestinal Symptoms After COVID-19
PubMed ID: 36049050
Lower microbial Trp production and plasma serotonin in acute COVID associated with later persistent mood symptoms (associative evidence).
- Investigation of the Effect of Tai Chi Training on Depressive Symptoms in Perimenopausal Women on the Basis of Serum Kynurenine Metabolites
PubMed ID: 39023066
Tai Chi reduced depressive symptoms and normalized kynurenine‑pathway metabolites linked to Trp metabolism.
- Metabolomics signatures of serotonin reuptake inhibitor (escitalopram), serotonin norepinephrine reuptake inhibitor (duloxetine) and cognitive-behavioral therapy on key neurotransmitter pathways in major depressive disorder
PubMed ID: 39818336
Metabolomics in MDD linked changes in Trp‑derived indoles/serotonin with antidepressant response (associative evidence).
- The effect of date seed powder supplementation on anxiety- and depression-like behaviours, sleep quality and tryptophan-kynurenine metabolism in patients with type 2 diabetes: targeting gut-brain axis
PubMed ID: 41157892
Date seed RCT raised TRP/ lowered KYN and produced mood and sleep improvements with reduced cortisol.
- Effect of hormone therapy on tryptophan metabolism and atherosclerosis among postmenopausal women
PubMed ID: 40512395
Estradiol reduced kynurenine‑pathway metabolites linked to better vascular outcomes; kynurenines affect brain function and mood.
- The Impact of 5-Hydroxytryptophan Supplementation on Cognitive Function and Mood in Singapore Older Adults: A Randomized Controlled Trial
PubMed ID: 40944161
5‑HTP (downstream of Trp) increased serum serotonin and produced small improvements in cognition and depressive symptoms in older adults.
- The effect of acupuncture on depression and its correlation with metabolic alterations: A randomized controlled trial
PubMed ID: 33120777
Electroacupuncture + antidepressants improved depression and changed urinary tryptophan/melatonin‑precursor metabolites — links tryptophan pathway changes to mood improvement.
- Effect of probiotic and prebiotic vs placebo on psychological outcomes in patients with major depressive disorder: A randomized clinical trial
PubMed ID: 29731182
Probiotic RCT in depressed patients reduced K/T ratio and produced clinically meaningful reductions in depressive symptoms, implicating improved TRP availability and mood.
- Integrated metabolomic insights into the mechanism of Bacillus coagulans in enhancing intestinal recovery following gynecological laparoscopic surgery: a randomized clinical trial
PubMed ID: 41080557
Perioperative probiotic increased plasma serotonin and shifted Trp/kynurenine pathways—relevant to mood regulation.
- Angry cognitive bias, trait aggression and impulsivity in substance users
PubMed ID: 13680074
Lowered serotonin via TRP depletion tended to increase aggressive/angry cognitive bias; supplementation plausibly reduces irritability.
- Rapid serotonin depletion as a provocative challenge test for patients with major depression: relevance to antidepressant action and the neurobiology of depression
PubMed ID: 1775606
Large controlled provocation: TRP depletion induced depressive relapses, with antidepressant-class differences (robust mood effect).
- Effects of food on cortisol and mood in vulnerable subjects under controllable and uncontrollable stress
PubMed ID: 11006432
A diet that raises plasma tryptophan (carb‑rich, low‑protein) lowered cortisol and feelings of depression in stress‑prone subjects.
- Comparative study of efficacy of l-5-hydroxytryptophan and fluoxetine in patients presenting with first depressive episode
PubMed ID: 23380314
l-5-HTP (tryptophan-derived) reduced depression scores comparably to fluoxetine in first-episode depressed patients (randomized DBS trial).
- Serotonin versus catecholamine deficiency: behavioral and neural effects of experimental depletion in remitted depression
PubMed ID: 25781231
Acute tryptophan depletion precipitated depressive symptoms in remitted depressed patients—supports Trp role in maintaining mood.
- Associations between expression of indoleamine 2, 3-dioxygenase enzyme and inflammatory cytokines in patients with first-episode drug-naive Schizophrenia
PubMed ID: 34802039
Lowering peripheral IDO (Trp catabolism) with celecoxib associated with improvement in negative symptoms (emotional/affect domain).
- Oxytocinergic Modulation of Threat-Specific Amygdala Sensitization in Humans Is Critically Mediated by Serotonergic Mechanisms
PubMed ID: 33894423
Central serotonin (ATD) attenuated oxytocin's amygdala desensitizing effect—links Trp/5‑HT to social threat processing and social ease.
- Functional Training Mitigates Reduced Circulating Indole-3-Lactate Levels in Persons With Relapsing-Remitting Multiple Sclerosis
PubMed ID: 41606419
Exercise increased neuroprotective Trp indoles (ILA) and ILA/IAA index, changes plausibly beneficial for emotional balance.
Stress & Anxiety (35)
- The effects of tryptophan depletion on neural responses to emotional words in remitted depression
PubMed ID: 19539268
ATD modulated limbic/habenula activity linked to negative bias—evidence TRP affects baseline emotional tone.
- Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress
PubMed ID: 18551283
ATD increased stress-related negative bias under stress in susceptible subjects, implying TRP helps anxiety/stress resilience.
- Effects of carbohydrates on brain tryptophan availability and stress performance
PubMed ID: 17689173
Improved mood/performance under stress with TRP-raising carbs supports reduced reactivity and greater mental calm.
- Differential effects of 5-HTTLPR genotypes on the behavioral and neural responses to tryptophan depletion in patients with major depression and controls
PubMed ID: 16953000
Genotype-dependent limbic/metabolic changes with TD implicate Trp in neural systems that underlie calmness and affect regulation.
- Effect of tryptophan depletion on smokers and nonsmokers with and without history of major depression
PubMed ID: 16893526
ATD provoked depressive symptoms in vulnerable individuals, indicating Trp availability is important for maintaining calm affective state.
- Tryptophan supplementation induces a positive bias in the processing of emotional material in healthy female volunteers
PubMed ID: 16767422
Positive emotional processing and reduced negative vigilance in women after Trp — contributes to emotional calm.
- Protein source tryptophan versus pharmaceutical grade tryptophan as an efficacious treatment for chronic insomnia
PubMed ID: 16053244
Improved sleep in insomnia trial would be expected to raise daytime calmness and reduce hyperarousal.
- Neural and behavioral responses to tryptophan depletion in unmedicated patients with remitted major depressive disorder and controls
PubMed ID: 15289275
TRP depletion reinstated depressive symptoms with limbic hyperactivity; keeping TRP available is likely to support calm affective states in vulnerable individuals.
- Association between serotonin transporter gene promoter polymorphism (5HTTLPR) and behavioral responses to tryptophan depletion in healthy women with and without family history of depression
PubMed ID: 12090814
Genotype‑dependent depressive/anxiety responses to TRP depletion indicate TRP's role in anxiety vulnerability.
- Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders
PubMed ID: 8080345
TRP depletion produced mood drops in vulnerable individuals—supports that adequate Trp helps maintain calmer mental state.
- Tryptophan and high-carbohydrate diets as adjuncts to smoking cessation therapy
PubMed ID: 1880796
Tryptophan (with counseling) lessened anxiety and some withdrawal symptoms in smokers (clinical anxiety reduction reported).
- Effects of acute treatment with a tryptophan-rich protein hydrolysate on plasma amino acids, mood and emotional functioning in older women
PubMed ID: 24858376
Acute Trp hydrolysate reduced fatigue and shifted emotional processing away from negative cues.
- Metabolome-associated psychological comorbidities improvement in irritable bowel syndrome patients receiving a probiotic
PubMed ID: 38717445
Probiotic increased circulating TRP metabolites and correlated with reduced amygdala reactivity and improved anxiety/depression scores (clinical+imaging link).
- Effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reaction in patients with post-stroke depression
PubMed ID: 39112627
Phototherapy raised plasma Trp and improved depressive/quality‑of‑life scores in post‑stroke patients.
- Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women
PubMed ID: 25572038
Altered emotional bias away from negative stimuli and faster, more accurate responding point to improved emotional regulation and calmer mental state in healthy adults.
- Oxytocinergic Modulation of Threat-Specific Amygdala Sensitization in Humans Is Critically Mediated by Serotonergic Mechanisms
PubMed ID: 33894423
ATD attenuated oxytocin‑induced amygdala desensitization; central 5‑HT availability modulates threat processing (anxiety mechanism).
- 5-Hydroxytryptophan as adjuvant therapy in treatment of moderate to severe obsessive-compulsive disorder: a double-blind randomized trial with placebo control
PubMed ID: 32541380
5‑HTP augmentation improved OCD symptoms (anxiety-related disorders) — serotonergic augmentation relevant to anxiety.
- Serotonin versus catecholamine deficiency: behavioral and neural effects of experimental depletion in remitted depression
PubMed ID: 25781231
ATD provoked depressive symptoms/emotional dysregulation—opposite effect suggests Trp supports emotional stability and calm.
- Acute L-5-hydroxytryptophan administration inhibits carbon dioxide-induced panic in panic disorder patients
PubMed ID: 12559480
Acute 5-HTP reduced CO2-challenge-induced anxiety and panic symptoms in panic disorder patients—direct, strong anxiolytic signal in a clinical model.
- Effect of acute tryptophan depletion on CO2-induced anxiety in patients with panic disorder and normal volunteers
PubMed ID: 10755058
Tryptophan depletion markedly increased CO2‑provoked panic and anxiety in panic disorder patients, implying adequate tryptophan reduces provoked anxiety/panic vulnerability.
- Effect of acute tryptophan depletion on behavioral, cardiovascular, and hormonal sensitivity to cholecystokinin-tetrapeptide challenge in healthy volunteers
PubMed ID: 8886299
Lowering TRP increased neuroendocrine stress-hormone responses to panic challenge, indicating reduced stress/anxiety resilience when TRP is low.
- Rapid serotonin depletion as a provocative challenge test for patients with major depression: relevance to antidepressant action and the neurobiology of depression
PubMed ID: 1775606
Large provocation study showed mood/anxiety vulnerability with TRP depletion across antidepressant classes (strong mechanistic evidence).
- Feed your microbes to deal with stress: a psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population
PubMed ID: 36289300
Psychobiotic diet lowered perceived stress and neurotoxic kynurenine metabolites—supports improved mental calmness via Trp pathway modulation.
- Supplementation with whey peptide rich in β-lactolin improves trait anxiety and subjective stress in healthy adults: a randomized, double-blind, placebo-controlled study
PubMed ID: 39379481
Whey peptide supplement (contains TRP residues) reduced trait anxiety and perceived stress in a randomized trial.
- The effect of date seed powder supplementation on anxiety- and depression-like behaviours, sleep quality and tryptophan-kynurenine metabolism in patients with type 2 diabetes: targeting gut-brain axis
PubMed ID: 41157892
Date seed RCT lowered cortisol, altered TRP/KYN and improved mood/sleep—consistent with increased mental calmness.
- The Usefulness of the Low-FODMAP Diet with Limited Tryptophan Intake in the Treatment of Diarrhea-Predominant Irritable Bowel Syndrome
PubMed ID: 37111056
Tryptophan‑restricted diet produced larger improvements in HAM‑A scores vs low‑FODMAP alone (clinical trial manipulating TRP intake).
- [Effect of acupuncture-moxibustion on negative emotions and plasma tryptophan metabolism in patients with Crohn's disease at active stage]
PubMed ID: 33559436
Acupuncture+moxibustion reduced HADS‑A (anxiety) with concurrent Trp–Kyn modulation in Crohn’s patients.
- Serotonin depletion amplifies distinct human social emotions as a function of individual differences in personality
PubMed ID: 33518708
ATD amplified negative social emotions (inverse evidence that sufficient Trp supports calmer mental states).
- SLC6A4 polymorphisms modulate the efficacy of a tryptophan-enriched diet on age-related depression and social cognition
PubMed ID: 33743283
Dietary tryptophan produced mood/empathy benefits in a responder genotype, consistent with improved emotional regulation and mental calmness in those individuals.
- Bifidobacterium breve CCFM1025 attenuates major depression disorder via regulating gut microbiome and tryptophan metabolism: A randomized clinical trial
PubMed ID: 34875345
Probiotic RCT lowered depressive scores and altered Trp/serotonin metabolism — strong signal for increased calmness.
- Acute tryptophan loading decreases functional connectivity between the default mode network and emotion-related brain regions
PubMed ID: 30585373
Acute tryptophan loading reduced DMN connectivity with emotion regions — a neural signature consistent with increased mental calmness (mechanistic evidence).
- Interaction between 5-HTTLPR genotype and cognitive stress vulnerability on sleep quality: effects of sub-chronic tryptophan administration
PubMed ID: 25644221
Improved sleep quality in stress‑vulnerable participants implies less hyperarousal and greater mental calmness.
- Functional Training Mitigates Reduced Circulating Indole-3-Lactate Levels in Persons With Relapsing-Remitting Multiple Sclerosis
PubMed ID: 41606419
Exercise‑induced increases in neuroprotective Trp indoles (ILA) are consistent with improved mental calm and resilience.
- Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism
PubMed ID: 24845181
Subchronic Trp reduced stress‑induced cortisol in genetically susceptible individuals—physiological support for anxiolytic effect.
- Effects of melatonin and tryptophan on healing of gastric and duodenal ulcers with Helicobacter pylori infection in humans
PubMed ID: 22204799
Increased melatonin after tryptophan supports relaxation and calmer mental state via improved sleep and parasympathetic effects.
Wellbeing (28)
- Effects of carbohydrates on brain tryptophan availability and stress performance
PubMed ID: 17689173
Carbohydrate-induced TRP availability improved mood and stress-task performance, reflecting improved subjective well‑being under challenge.
- Effect of tryptophan depletion on smokers and nonsmokers with and without history of major depression
PubMed ID: 16893526
ATD precipitated depressive symptoms in vulnerable individuals, implying normal Trp contributes to subjective well‑being.
- Neural and behavioral responses to tryptophan depletion in unmedicated patients with remitted major depressive disorder and controls
PubMed ID: 15289275
TRP depletion produced symptom relapse in remitted MDD; maintaining TRP availability is therefore plausibly tied to subjective well‑being.
- Association between serotonin transporter gene promoter polymorphism (5HTTLPR) and behavioral responses to tryptophan depletion in healthy women with and without family history of depression
PubMed ID: 12090814
Genotype‑dependent mood vulnerability during TRP depletion suggests TRP contributes to subjective well‑being.
- A placebo-controlled clinical trial of L-tryptophan in premenstrual dysphoria
PubMed ID: 10023508
L-tryptophan improved luteal-phase mood clusters, consistent with better subjective well‑being.
- Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders
PubMed ID: 8080345
TRP depletion caused clinically meaningful mood drops in at‑risk men—evidence that Trp supports well‑being.
- Effects of acute treatment with a tryptophan-rich protein hydrolysate on plasma amino acids, mood and emotional functioning in older women
PubMed ID: 24858376
Acute Trp hydrolysate prevented declines in wellbeing and reduced fatigue.
- Effect of Talbinah food consumption on depressive symptoms among elderly individuals in long term care facilities, randomized clinical trial
PubMed ID: 23493965
Talbinah produced clinically meaningful reductions in depressive symptoms and improved multiple mood subscales in elderly residents.
- Effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reaction in patients with post-stroke depression
PubMed ID: 39112627
Phototherapy raised plasma Trp and improved depressive and QoL scores after stroke.
- Tryptophan-depletion challenge in depressed patients treated with desipramine or fluoxetine: implications for the role of serotonin in the mechanism of antidepressant action
PubMed ID: 10418696
TRP depletion triggered relapse in SSRI-treated (fluoxetine) responders, linking TRP to maintained antidepressant benefit and well‑being.
- Tryptophan supplementation induces a positive bias in the processing of emotional material in healthy female volunteers
PubMed ID: 16767422
Two‑week Trp shifted emotional processing positively in healthy women, consistent with enhanced well‑being.
- Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women
PubMed ID: 25572038
Positive shift in emotional processing and modest increases in energy and response speed suggest an enhanced subjective sense of well‑being.
- Food can lift mood by affecting mood-regulating neurocircuits via a serotonergic mechanism
PubMed ID: 24076224
Acute Trp‑enriched drink produced subjective mood lift and brain changes in reward/affect circuits consistent with improved well‑being.
- Effects of melatonin and tryptophan on healing of gastric and duodenal ulcers with Helicobacter pylori infection in humans
PubMed ID: 22204799
Tryptophan raised melatonin and produced clinical improvements in an adjunct setting; improved sleep often translates into enhanced well‑being.
- Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress
PubMed ID: 18551283
ATD reduced positive affective responsiveness under stress, indicating TRP supports positive emotionality.
- Serotonin transporter genotype and depressive phenotype determination by discriminant analysis of glucose metabolism under acute tryptophan depletion
PubMed ID: 18718871
ATD-induced relapse in remitted depression shows TRP availability underpins sustained well-being.
- Differential effects of 5-HTTLPR genotypes on the behavioral and neural responses to tryptophan depletion in patients with major depression and controls
PubMed ID: 16953000
Tryptophan depletion produced genotype-dependent changes in limbic metabolism and mood, linking Trp to subjective affect.
- Serotonin versus catecholamine deficiency: behavioral and neural effects of experimental depletion in remitted depression
PubMed ID: 25781231
ATD induced depressive symptom domains, implying Trp helps maintain subjective well‑being.
- Comparative study of efficacy of l-5-hydroxytryptophan and fluoxetine in patients presenting with first depressive episode
PubMed ID: 23380314
l-5-HTP produced substantial antidepressant responses comparable to fluoxetine, consistent with improved well-being.
- Rapid serotonin depletion as a provocative challenge test for patients with major depression: relevance to antidepressant action and the neurobiology of depression
PubMed ID: 1775606
Large study showing mood relapse with TRP depletion supports TRP role in well-being.
- Double-blind study of 5-hydroxytryptophan versus placebo in the treatment of primary fibromyalgia syndrome
PubMed ID: 2193835
5-HTP improved fibromyalgia clinical parameters and tolerability, enhancing well-being in that population.
- Integrated metabolomic insights into the mechanism of Bacillus coagulans in enhancing intestinal recovery following gynecological laparoscopic surgery: a randomized clinical trial
PubMed ID: 41080557
Shifts toward serotonin and favourable Trp metabolomics after probiotic were associated with better postoperative recovery signals.
- Effect of probiotic and prebiotic vs placebo on psychological outcomes in patients with major depressive disorder: A randomized clinical trial
PubMed ID: 29731182
Probiotic trial in depressed patients reduced depressive scores and K/T ratio, which translates to improved well-being tied to TRP metabolism.
- The effect of acupuncture on depression and its correlation with metabolic alterations: A randomized controlled trial
PubMed ID: 33120777
Adjunctive electroacupuncture produced larger reductions in depression and altered tryptophan‑related metabolites — supports enhanced well‑being via tryptophan pathway.
- The effect of date seed powder supplementation on anxiety- and depression-like behaviours, sleep quality and tryptophan-kynurenine metabolism in patients with type 2 diabetes: targeting gut-brain axis
PubMed ID: 41157892
Date seed powder improved mood and sleep, lowered cortisol and modulated TRP→KYN metabolism — consistent with greater well‑being.
- SLC6A4 polymorphisms modulate the efficacy of a tryptophan-enriched diet on age-related depression and social cognition
PubMed ID: 33743283
Subjective mood/empathy gains with dietary tryptophan in a genetic subgroup support enhanced well‑being for those responders.
- Bifidobacterium breve CCFM1025 attenuates major depression disorder via regulating gut microbiome and tryptophan metabolism: A randomized clinical trial
PubMed ID: 34875345
Depressive symptom reductions and Trp/serotonin pathway changes consistent with improved well‑being.
- Effect of Tryptophan, Vitamin B(6), and Nicotinamide-Containing Supplement Loading between Meals on Mood and Autonomic Nervous System Activity in Young Adults with Subclinical Depression: A Randomized, Double-Blind, and Placebo-Controlled Study
PubMed ID: 31902864
Observed improvements in depressive mood and some POMS domains indicate an enhanced sense of well‑being in the treated subgroup.
Stress resilience (23)
- Dietary tryptophan effects on plasma and salivary cortisol and meat quality in pigs
PubMed ID: 16864887
Extra dietary Trp in pigs lowered plasma cortisol and lactate, indicating reduced stress-related physiological responses (animal model).
- Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders
PubMed ID: 8080345
TRP depletion provoked mood drops in genetically vulnerable subjects—indicates Trp availability can modulate stress-related mood responses.
- Whey protein rich in alpha-lactalbumin increases the ratio of plasma tryptophan to the sum of the other large neutral amino acids and improves cognitive performance in stress-vulnerable subjects
PubMed ID: 12036812
TRP‑rich diet improved cognitive performance in stress‑vulnerable subjects — suggests resilience to stress‑related cognitive decline.
- The Effects of Tryptophan Enhancement and Depletion on Plasma Catecholamine Levels in Healthy Individuals
PubMed ID: 30188382
Raising CNS tryptophan increased epinephrine but lowered norepinephrine and raised prolactin/cortisol; these neuroendocrine changes indicate tryptophan can alter stress responses.
- Effects of stress and dietary tryptophan enhancement on craving for alcohol in binge and non-binge heavy drinkers
PubMed ID: 25036731
Trp intake modified stress effects on craving and heart rate—evidence of altered stress responsivity (subgroup differences).
- Tryptophan-depletion challenge in depressed patients treated with desipramine or fluoxetine: implications for the role of serotonin in the mechanism of antidepressant action
PubMed ID: 10418696
TRP depletion caused relapse on SSRI (fluoxetine) treatment, showing TRP's role in maintaining treatment resilience.
- Investigation of the Effect of Tai Chi Training on Depressive Symptoms in Perimenopausal Women on the Basis of Serum Kynurenine Metabolites
PubMed ID: 39023066
Tai Chi decreased kynurenine pathway markers and depressive symptoms; mind‑body intervention demonstrated improved stress‑related biology.
- Impact of a Specific Amino Acid Composition with Micronutrients on Well-Being in Subjects with Chronic Psychological Stress and Exhaustion Conditions: A Pilot Study
PubMed ID: 29710825
Multi‑AA + micronutrient supplement reduced perceived stress and increased l‑tryptophan/CAA ratio over 12 weeks (clinical stress outcome; attribution limited).
- Feed your microbes to deal with stress: a psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population
PubMed ID: 36289300
Psychobiotic diet significantly reduced perceived stress and lowered quinolinic acid (KP metabolite linked to stress susceptibility).
- Rapid serotonin depletion as a provocative challenge test for patients with major depression: relevance to antidepressant action and the neurobiology of depression
PubMed ID: 1775606
TRP depletion increased relapse vulnerability differentially by antidepressant class, implicating TRP/serotonin in stress-related resilience.
- Effect of acute tryptophan depletion on behavioral, cardiovascular, and hormonal sensitivity to cholecystokinin-tetrapeptide challenge in healthy volunteers
PubMed ID: 8886299
Lowering TRP enhanced ACTH/cortisol and prolactin responses to a panicogenic challenge, indicating TRP supports neuroendocrine stress control.
- Carbohydrate intake improves cognitive performance of stress-prone individuals under controllable laboratory stress
PubMed ID: 10690161
Dietary increases in tryptophan availability improved cognitive outcomes after stress in vulnerable subjects.
- Effects of food on cortisol and mood in vulnerable subjects under controllable and uncontrollable stress
PubMed ID: 11006432
A diet increasing plasma tryptophan blunted cortisol responses and lowered depressive mood in stress‑prone individuals, indicating improved stress resilience.
- Oxytocinergic Modulation of Threat-Specific Amygdala Sensitization in Humans Is Critically Mediated by Serotonergic Mechanisms
PubMed ID: 33894423
ATD reduced oxytocin’s amygdala‑desensitizing effect; central 5‑HT availability modulates adaptive threat processing (stress resilience mechanism).
- Functional Training Mitigates Reduced Circulating Indole-3-Lactate Levels in Persons With Relapsing-Remitting Multiple Sclerosis
PubMed ID: 41606419
10‑week training increased ILA/IAA index and acute increases in ILA—indole changes linked to neuroprotection and resilience.
- The effect of date seed powder supplementation on anxiety- and depression-like behaviours, sleep quality and tryptophan-kynurenine metabolism in patients with type 2 diabetes: targeting gut-brain axis
PubMed ID: 41157892
Date seed powder lowered cortisol and KYN:TRP ratio while improving mood/sleep—consistent with improved stress resilience.
- Fermented milk containing Lactobacillus casei strain Shirota prevents the onset of physical symptoms in medical students under academic examination stress
PubMed ID: 26689231
Probiotic prevented stress‑linked cortisol increase and modulated plasma Trp/serotonin signals in stressed students—suggests Trp pathway involvement in stress responses.
- Stress mitigating and growth enhancing effect of dietary tryptophan in rohu (Labeo rohita, Hamilton, 1822) fingerlings
PubMed ID: 24705914
Dietary L‑tryptophan lowered cortisol and improved growth in heat‑stressed fish—evidence TRP mitigates physiological stress responses (animal data).
- Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism
PubMed ID: 24845181
Subchronic oral Trp blunted stress‑induced cortisol responses in 5‑HTTLPR S/S individuals—direct physiological marker of stress resilience.
- The effect of tryptophan on the cortisol response to social stress is modulated by the 5-HTTLPR genotype
PubMed ID: 22717170
6‑day L‑tryptophan (2.8 g/day) significantly lowered salivary cortisol response to Trier Social Stress Test in susceptible genotype carriers → direct stress‑resilience effect.
- The effects of tryptophan depletion on neural responses to emotional words in remitted depression
PubMed ID: 19539268
ATD altered limbic/habenula responses tied to negative bias under emotional challenges.
- Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress
PubMed ID: 18551283
ATD increased stress-related negative affective bias, implying TRP supports stress resilience.
- Effects of carbohydrates on brain tryptophan availability and stress performance
PubMed ID: 17689173
Carbohydrate-induced TRP availability improved both mood and task performance during experimental stress, indicating better stress resilience.
Sleep quality (21)
- Effects of melatonin and tryptophan on healing of gastric and duodenal ulcers with Helicobacter pylori infection in humans
PubMed ID: 22204799
Oral tryptophan raised plasma melatonin and was associated with clinical benefits (ulcer healing context) — strong mechanistic link to improved sleep via melatonin synthesis.
- Interaction between 5-HTTLPR genotype and cognitive stress vulnerability on sleep quality: effects of sub-chronic tryptophan administration
PubMed ID: 25644221
Seven days oral tryptophan improved PSQI sleep quality in stress‑/genetically vulnerable humans (direct trial).
- Tryptophan for the sleeping disorder and mental symptom of new-type drug dependence: A randomized, double-blind, placebo-controlled trial
PubMed ID: 27428201
Two‑week oral tryptophan produced significant AIS (insomnia) improvement in detoxified patients (randomized trial).
- The serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the sleep-promoting effects of tryptophan: A randomized placebo-controlled crossover study
PubMed ID: 31237183
1 g nightly tryptophan RCT (n=98) improved objective sleep efficiency and reduced WASO — direct, moderate‑strength sleep benefit.
- Use of nutritional supplements based on melatonin, tryptophan and vitamin B6 (Melamil Tripto®) in children with primary chronic headache, with or without sleep disorders: a pilot study
PubMed ID: 31621274
Children with headaches: adding tryptophan+melatonin+B6 reduced night awakenings vs melatonin alone — supportive though combined intervention limits attribution solely to tryptophan.
- Optimisation and Validation of a Nutritional Intervention to Enhance Sleep Quality and Quantity
PubMed ID: 32854375
α-lactalbumin–containing drink (Trp source) shortened sleep onset and raised blood free Trp in an RCT—strong sleep benefit though multi-ingredient.
- Mulberry leaf extract combined with tryptophan improves sleep and post wake mood in adults with sleep complaints - A randomized cross-over study
PubMed ID: 40072601
Evening multi‑ingredient supplement containing tryptophan shortened sleep onset and improved next‑day mood in crossover trial.
- The effect of date seed powder supplementation on anxiety- and depression-like behaviours, sleep quality and tryptophan-kynurenine metabolism in patients with type 2 diabetes: targeting gut-brain axis
PubMed ID: 41157892
Date seed powder raised TRP and lowered KYN while improving mood and sleep measures in an 8‑week RCT in T2DM.
- Melatonin decreases delirium in elderly patients: a randomized, placebo-controlled trial
PubMed ID: 20845391
Low-dose nightly melatonin (tryptophan-derived hormone) halved delirium in elderly inpatients and supports sleep-related outcomes.
- The impact of 5-hydroxytryptophan supplementation on sleep quality and gut microbiota composition in older adults: A randomized controlled trial
PubMed ID: 38309227
Randomized 12‑week 5‑HTP increased serum serotonin and significantly improved PSQI global sleep score in poor‑sleep older adults.
- Improvement of sleep by resistant dextrin prebiotic in type 2 diabetic women coincides with attenuation of metabolic endotoxemia: involvement of gut-brain axis
PubMed ID: 35306660
Resistant‑dextrin prebiotic improved PSQI and correlations between sleep quality and KYN/TRP were reported (indirect TRP axis link).
- L -5-Hydroxytryptophan treatment of sleep terrors in children
PubMed ID: 15146330
Nightly 5‑HTP in children produced large, lasting reduction in sleep terrors (open‑label) — strong effect on clinically disruptive sleep.
- Infant growth and tolerance with a formula based on novel native demineralized whey: A randomized double-blind pilot study
PubMed ID: 38988234
Infant formula raising plasma tryptophan increased sleep duration at several ages (direct nutritional Trp → sleep effect).
- Effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reaction in patients with post-stroke depression
PubMed ID: 39112627
Phototherapy raised plasma tryptophan and improved depression/quality‑of‑life including sleep‑related scores post‑stroke (TRP increase correlated with symptoms).
- Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial
PubMed ID: 40791136
Walnut intake (dietary Trp source) raised urinary melatonin metabolite and improved sleep latency/quality in young adults.
- Preliminary randomized double-blind placebo-controlled trial of tryptophan combined with fluoxetine to treat major depressive disorder: antidepressant and hypnotic effects
PubMed ID: 11022398
Tryptophan added to fluoxetine protected slow‑wave sleep at 4 weeks (preservation of deep sleep), supporting a sleep‑benefit when combined with SSRI in this trial.
- Protein source tryptophan versus pharmaceutical grade tryptophan as an efficacious treatment for chronic insomnia
PubMed ID: 16053244
Randomized double‑blind trial: both protein‑source and pharmaceutical tryptophan + carbohydrate improved objective and subjective sleep in chronic insomnia.
- [The effect of amino acid nutritional support on serum tryptophan and melatonin in lung cancer patients receiving chemotherapy]
PubMed ID: 17416006
Parenteral amino acids during chemo preserved serum tryptophan and melatonin — mechanistic support for improved sleep.
- Chrononutrition applied to formula milks to consolidate infants' sleep/wake cycle
PubMed ID: 17693960
Infant day/night formula (higher night Trp among other changes) increased nocturnal sleep and reduced latency — clinically relevant sleep improvement.
- Improving the quality of infant sleep through the inclusion at supper of cereals enriched with tryptophan, adenosine-5'-phosphate, and uridine-5'-phosphate
PubMed ID: 19925721
Infant randomized crossover: tryptophan-enriched evening cereal reduced night wakings and improved multiple sleep parameters.
- Melatonin or L-tryptophan accelerates healing of gastroduodenal ulcers in patients treated with omeprazole
PubMed ID: 21362032
Tryptophan adjunct markedly increased plasma melatonin and produced clinical benefit; mechanistically supports sleep improvement.
Mental clarity (15)
- Effects of acute tryptophan depletion on neuropsychological and motor function in Parkinson's disease
PubMed ID: 19460872
ATD produced differential cognitive effects in Parkinson's vs controls, indicating TRP influences cognitive function.
- Valence-dependent influence of serotonin depletion on model-based choice strategy
PubMed ID: 25869808
ATD produced a shift from model‑based (goal‑directed) to model‑free choices, implying Trp/serotonin supports goal‑directed (clearer) decision making.
- Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women
PubMed ID: 25572038
Shortened reaction times and increased processing speed were observed with a TRP‑rich hydrolysate in healthy adults—evidence for improved mental processing.
- Effect of Supplementation of a Whey Peptide Rich in Tryptophan-Tyrosine-Related Peptides on Cognitive Performance in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Study
PubMed ID: 30011836
Whey‑peptide supplement containing tryptophan‑rich peptides improved verbal fluency and attention/executive measures in high‑fatigue participants.
- The Impact of 5-Hydroxytryptophan Supplementation on Cognitive Function and Mood in Singapore Older Adults: A Randomized Controlled Trial
PubMed ID: 40944161
5‑HTP increased serum serotonin and produced a small but significant MoCA cognitive screening improvement in older adults.
- Probiotic Lactobacillus Plantarum 299v decreases kynurenine concentration and improves cognitive functions in patients with major depression: A double-blind, randomized, placebo controlled study
PubMed ID: 30388595
Probiotic adjunct to SSRI lowered kynurenine and improved attention/verbal learning, linking TRP metabolism changes to clearer cognitive function.
- Carbohydrate intake improves cognitive performance of stress-prone individuals under controllable laboratory stress
PubMed ID: 10690161
A meal that increases plasma tryptophan availability improved cognitive performance in stress‑prone young adults after controllable stress.
- Serotonin depletion impairs both Pavlovian and instrumental reversal learning in healthy humans
PubMed ID: 34429517
Acute tryptophan depletion (ATD) impaired cognitive/reversal learning, implying adequate tryptophan supports cognitive flexibility and clearer thinking.
- Acute dietary tryptophan depletion impairs maintenance of "affective set" and delayed visual recognition in healthy volunteers
PubMed ID: 11351939
Depletion disrupted delayed visual recognition and affective‑attentional tasks in healthy volunteers (selective cognitive impairments).
- Cognition following acute tryptophan depletion: difference between first-degree relatives of bipolar disorder patients and matched healthy control volunteers
PubMed ID: 11989995
ATD slowed processing and harmed long‑term memory, especially in at‑risk relatives — supports TRP importance for cognition.
- Altered response to tryptophan supplementation after long-term abstention from MDMA (ecstasy) is highly correlated with human memory function
PubMed ID: 12759801
In ex-MDMA users, TRP raised blood TRP and was linked to improved delayed memory, consistent with benefits to cognitive function.
- Whey protein rich in alpha-lactalbumin increases the ratio of plasma tryptophan to the sum of the other large neutral amino acids and improves cognitive performance in stress-vulnerable subjects
PubMed ID: 12036812
Tryptophan‑rich whey increased TRP availability and improved memory scanning in stress‑vulnerable subjects — clear cognitive improvement.
- Effects of acute tryptophan depletion on mood and cognitive functioning in older recovered depressed subjects
PubMed ID: 16009737
Acute tryptophan depletion caused a measurable drop in cognitive screening (MMSE) in older recovered-depressed subjects, indicating Trp supports cognitive function.
- Effects of acute tryptophan depletion on cognition, memory and motor performance in Parkinson's disease
PubMed ID: 16756999
ATD impaired delayed verbal memory — supports role of Trp/serotonin in episodic memory relevant to clear thinking.
- The role of serotonin in nonnormative risky choice: the effects of tryptophan supplements on the "reflection effect" in healthy adult volunteers
PubMed ID: 18823228
Tryptophan supplementation (3 g/day) reduced an irrational bias in risky choice and changed weighting of gains/losses — cognitive decision benefit.
Sleep onset (11)
- [The effect of amino acid nutritional support on serum tryptophan and melatonin in lung cancer patients receiving chemotherapy]
PubMed ID: 17416006
Parenteral AA preserved melatonin levels during chemo — mechanistic support for facilitating sleep onset.
- Protein source tryptophan versus pharmaceutical grade tryptophan as an efficacious treatment for chronic insomnia
PubMed ID: 16053244
Insomnia trial with TRP+carbohydrate improved objective and subjective sleep; faster sleep onset is a plausible component of the overall sleep benefit.
- Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial
PubMed ID: 40791136
Walnut intake reduced sleep latency and increased melatonin metabolite—direct evidence for faster sleep onset.
- Effects of melatonin and tryptophan on healing of gastric and duodenal ulcers with Helicobacter pylori infection in humans
PubMed ID: 22204799
Tryptophan increased plasma melatonin markedly — a direct promoter of sleep onset; strong mechanistic/clinical support.
- Optimisation and Validation of a Nutritional Intervention to Enhance Sleep Quality and Quantity
PubMed ID: 32854375
α-lactalbumin–based drink shortened sleep onset latency by ~49% in an RCT—strong direct evidence for faster sleep onset.
- Mulberry leaf extract combined with tryptophan improves sleep and post wake mood in adults with sleep complaints - A randomized cross-over study
PubMed ID: 40072601
Evening supplement containing tryptophan shortened sleep onset latency (actigraphy −3.82 min, self‑report −3.09 min) in crossover trial.
- L -5-Hydroxytryptophan treatment of sleep terrors in children
PubMed ID: 15146330
Nightly 5‑HTP reduced sleep terrors in children and improved sleep continuity — may facilitate falling asleep in affected children.
- Interaction between 5-HTTLPR genotype and cognitive stress vulnerability on sleep quality: effects of sub-chronic tryptophan administration
PubMed ID: 25644221
Short‑term Trp improved sleep quality in susceptible individuals; faster sleep onset plausibly contributed though not directly measured.
- Melatonin or L-tryptophan accelerates healing of gastroduodenal ulcers in patients treated with omeprazole
PubMed ID: 21362032
Adjunct tryptophan raised melatonin levels and accelerated clinical endpoints — supports faster sleep onset via melatonin pathway.
- Improving the quality of infant sleep through the inclusion at supper of cereals enriched with tryptophan, adenosine-5'-phosphate, and uridine-5'-phosphate
PubMed ID: 19925721
Evening tryptophan-enriched cereal reduced nocturnal wakings and improved sleep parameters; supports faster settling.
- Chrononutrition applied to formula milks to consolidate infants' sleep/wake cycle
PubMed ID: 17693960
Infant formula higher night Trp reduced sleep latency and increased nocturnal sleep — evidence for faster sleep onset (though multi‑component formula).
Appetite regulation (10)
- The Effects of 5-HTP on Body Composition: An 8-Week Preliminary RCT
PubMed ID: 35583055
5‑HTP reduced fat mass in RCT and is a serotonin precursor that can reduce appetite/energy intake.
- [The effect of consuming quality protein maize or conventional maize on the growth and morbidity of malnourished Nicaraguan children 1 to 5 years of age]
PubMed ID: 19368299
Quality-protein (higher-tryptophan) maize improved growth/nutritional status in children, supporting dietary TRP effects on appetite/nutrition.
- Effects of a Novel High-Quality Protein Infant Formula on Energetic Efficiency and Tolerance: A Randomized Trial
PubMed ID: 35666855
Alpha‑lactalbumin formula raised serum tryptophan and infants drank less while gaining efficiently (appetite/satiety effect).
- Effects of intragastric tryptophan on acute changes in the plasma tryptophan/large neutral amino acids ratio and relationship with subsequent energy intake in lean and obese men
PubMed ID: 32729586
Intragastric 3 g tryptophan raised Trp/LNAA and reduced subsequent energy intake in lean men—direct appetite/balance signal.
- Effects of Intragastric Administration of Tryptophan on the Blood Glucose Response to a Nutrient Drink and Energy Intake, in Lean and Obese Men
PubMed ID: 29642492
3.0 g intragastric L‑tryptophan slowed gastric emptying and reduced energy intake in ~50% of participants (direct appetite suppression).
- Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism
PubMed ID: 24845181
7‑day oral Trp blunted stress‑driven appetite increases in vulnerable (S/S) individuals.
- Acute tryptophan depletion increases experimental nausea but also induces hunger in healthy female subjects
PubMed ID: 20553564
Acute tryptophan depletion increased hunger in healthy women, implying normal tryptophan supports appetite regulation.
- Plasma amino acid ratios related to brain serotonin synthesis in response to food intake in bulimia nervosa
PubMed ID: 8555377
Meal-related Trp/LNAA changes correlated with lower lunchtime intake in bulimic subjects—moderate evidence linking Trp physiology to appetite.
- Evidence for brain serotonin-mediated control of carbohydrate consumption in normal weight and obese humans
PubMed ID: 8220653
Breakfast-induced Trp/LNAA changes influenced subsequent macronutrient choice, supporting appetite regulation mechanism.
- Physical exercise and normobaric hypoxia: independent modulators of peripheral cholecystokinin metabolism in man
PubMed ID: 11133899
Exercise-induced rises in free tryptophan ratio strongly correlated with large CCK increases (a satiety signal), linking tryptophan availability to appetite regulation.
Appetite suppression (9)
- Effects of Intragastric Administration of Tryptophan on the Blood Glucose Response to a Nutrient Drink and Energy Intake, in Lean and Obese Men
PubMed ID: 29642492
3 g intragastric tryptophan reduced subsequent energy intake in ~50% of subjects (direct reduction of intake/craving in responders).
- The Effects of 5-HTP on Body Composition: An 8-Week Preliminary RCT
PubMed ID: 35583055
8‑week 5‑HTP supplementation reduced fat mass in exercise‑trained adults, consistent with reduced intake/cravings mediated by serotonin.
- Effects of stress and dietary tryptophan enhancement on craving for alcohol in binge and non-binge heavy drinkers
PubMed ID: 25036731
Trp‑enriched meal blocked stress‑related increases in alcohol craving in binge drinkers (behavioral craving outcome; subgroup).
- Evidence for brain serotonin-mediated control of carbohydrate consumption in normal weight and obese humans
PubMed ID: 8220653
Meal composition altered Trp/LNAA and was associated with changes in carbohydrate intake at the next meal (mechanistic link to cravings).
- Plasma amino acid ratios related to brain serotonin synthesis in response to food intake in bulimia nervosa
PubMed ID: 8555377
Post-meal Trp/LNAA differences in bulimic women associated with lower lunchtime intake—moderate evidence Trp dynamics affect food intake/cravings.
- Impact of acute tryptophan depletion on mood and eating-related urges in bulimic and nonbulimic women
PubMed ID: 19721848
ATD increased urge to binge in SSRI-treated bulimic women, implying adequate TRP may suppress binge/craving urges.
- Acute tryptophan depletion increases experimental nausea but also induces hunger in healthy female subjects
PubMed ID: 20553564
ATD increased hunger in healthy women (inverse evidence that TRP sufficiency reduces hunger/craving).
- Effect of sub chronic tryptophan supplementation on stress-induced cortisol and appetite in subjects differing in 5-HTTLPR genotype and trait neuroticism
PubMed ID: 24845181
7‑day Trp prevented stress‑induced appetite increases in S/S genotype carriers, indicating reduced stress‑related cravings.
- Effects of intragastric tryptophan on acute changes in the plasma tryptophan/large neutral amino acids ratio and relationship with subsequent energy intake in lean and obese men
PubMed ID: 32729586
Acute intragastric Trp reduced subsequent energy intake in lean men—direct evidence for appetite/craving suppression.
Focus & concentration (8)
- Altered response to tryptophan supplementation after long-term abstention from MDMA (ecstasy) is highly correlated with human memory function
PubMed ID: 12759801
TRP supplementation improved delayed memory performance in ex-MDMA users, reflecting improved cognitive function including concentration.
- The short (S) allele of the serotonin transporter polymorphism and acute tryptophan depletion both increase impulsivity in men
PubMed ID: 20188795
ATD produced increased impulsivity and altered response bias — by reverse inference restoring tryptophan availability is likely to reduce impulsivity and improve focused responding.
- Valence-dependent influence of serotonin depletion on model-based choice strategy
PubMed ID: 25869808
ATD reduced model‑based decision weighting (cognitive control) suggesting Trp supports goal‑directed cognitive processes important for focus.
- Whey protein rich in alpha-lactalbumin increases the ratio of plasma tryptophan to the sum of the other large neutral amino acids and improves cognitive performance in stress-vulnerable subjects
PubMed ID: 12036812
Tryptophan‑rich protein improved memory scanning in stress‑vulnerable people — supports enhanced focused cognitive performance.
- Effect of Supplementation of a Whey Peptide Rich in Tryptophan-Tyrosine-Related Peptides on Cognitive Performance in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Study
PubMed ID: 30011836
Whey‑peptide supplement (containing tryptophan peptides) improved attention/executive tasks in participants with high subjective fatigue.
- Probiotic Lactobacillus Plantarum 299v decreases kynurenine concentration and improves cognitive functions in patients with major depression: A double-blind, randomized, placebo controlled study
PubMed ID: 30388595
Probiotic adjunct reduced kynurenine and improved attention measures in depressed patients, supporting improved concentration via TRP-pathway effects.
- Carbohydrate intake improves cognitive performance of stress-prone individuals under controllable laboratory stress
PubMed ID: 10690161
Raising tryptophan availability via meal composition improved cognitive performance after stress in stress‑prone subjects (better task performance).
- Serotonin depletion impairs both Pavlovian and instrumental reversal learning in healthy humans
PubMed ID: 34429517
ATD produced impairments in reversal learning and conditioned reversal, implying that normal tryptophan/serotonin supports aspects of cognitive control and concentration.
Relaxation (8)
- Acute L-5-hydroxytryptophan administration inhibits carbon dioxide-induced panic in panic disorder patients
PubMed ID: 12559480
Acute 5-HTP reduced experimentally induced panic/anxiety in panic disorder patients, consistent with increased relaxation.
- Feed your microbes to deal with stress: a psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population
PubMed ID: 36289300
Psychobiotic diet reduced perceived stress (a proxy for relaxation) and shifted kynurenine pathway metabolites.
- Postoperative pain treated by intravenous L-tryptophan: a double-blind study versus placebo in cholecystectomized patients
PubMed ID: 1762811
IV L-tryptophan reduced postoperative pain and produced longer relief at higher dose, consistent with increased relaxation/comfort.
- Neural and behavioral responses to tryptophan depletion in unmedicated patients with remitted major depressive disorder and controls
PubMed ID: 15289275
TRP depletion reinstated depressive symptoms and altered limbic activity; restoration of TRP could reduce arousal/tension in susceptible individuals.
- Protein source tryptophan versus pharmaceutical grade tryptophan as an efficacious treatment for chronic insomnia
PubMed ID: 16053244
Sleep improvements with TRP likely include increased relaxation; trial showed subjective sleep benefits.
- Melatonin or L-tryptophan accelerates healing of gastroduodenal ulcers in patients treated with omeprazole
PubMed ID: 21362032
Similar melatonin-raising effect with adjunct tryptophan supports relaxation-related benefits.
- Effects of melatonin and tryptophan on healing of gastric and duodenal ulcers with Helicobacter pylori infection in humans
PubMed ID: 22204799
Tryptophan-induced melatonin increases support relaxation and parasympathetic activity related to sleep and calmness.
- Interaction between 5-HTTLPR genotype and cognitive stress vulnerability on sleep quality: effects of sub-chronic tryptophan administration
PubMed ID: 25644221
Improved subjective sleep quality in stress‑vulnerable genotype indicates greater nocturnal relaxation/less arousal.
Energy & Fatigue (6)
- Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial
PubMed ID: 40791136
Walnut intake reduced daytime sleepiness and improved global sleep quality, supporting steadier daytime energy.
- Improving the quality of infant sleep through the inclusion at supper of cereals enriched with tryptophan, adenosine-5'-phosphate, and uridine-5'-phosphate
PubMed ID: 19925721
Improved infant night sleep can lead to steadier daytime energy (indirect but plausible).
- Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women
PubMed ID: 25572038
Participants reported increased arousal/'high energy' and showed faster reaction times after TRP hydrolysate supplementation—direct evidence for steadier/greater daytime energy.
- Hydrocortisone Affects Fatigue and Physical Functioning Through Metabolism of Tryptophan: A Randomized Controlled Trial
PubMed ID: 29982583
In secondary adrenal insufficiency, changes in hydrocortisone dose altered Kyn/Trp and this mediated improvements in fatigue and physical functioning — direct evidence linking TRP metabolism to daytime energy.
- Effects of a Novel High-Quality Protein Infant Formula on Energetic Efficiency and Tolerance: A Randomized Trial
PubMed ID: 35666855
Infants on alpha‑lactalbumin formula had higher Trp/LNAA ratios and greater energetic efficiency with lower intake (proxy for steadier energy availability).
- Nicotinamide modulates gut microbial metabolic potential and accelerates recovery in mild-to-moderate COVID-19
PubMed ID: 40355744
Nicotinamide accelerated physical recovery after COVID and altered gut microbial tryptophan/NAD+ pathways relevant to energy metabolism.
Exercise recovery (4)
- Dietary tryptophan effects on plasma and salivary cortisol and meat quality in pigs
PubMed ID: 16864887
Additional dietary Trp in pigs lowered plasma lactate and cortisol, physiological signals associated with improved recovery after exertion (animal evidence).
- Nicotinamide modulates gut microbial metabolic potential and accelerates recovery in mild-to-moderate COVID-19
PubMed ID: 40355744
Large RCT: nicotinamide accelerated recovery of physical performance after COVID and modulated gut tryptophan/NAD+ pathways.
- Integrated metabolomic insights into the mechanism of Bacillus coagulans in enhancing intestinal recovery following gynecological laparoscopic surgery: a randomized clinical trial
PubMed ID: 41080557
Perioperative probiotic shortened time to first defecation and altered Trp/5‑HT metabolites—direct clinical recovery benefit in surgical context.
- Functional Training Mitigates Reduced Circulating Indole-3-Lactate Levels in Persons With Relapsing-Remitting Multiple Sclerosis
PubMed ID: 41606419
Training increased ILA/IAA index and acute ILA rises after exercise (putative neuroprotective metabolite), suggesting improved recovery capacity.
Similar by evidence
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Products with Tryptophan
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