Back to Mental
Mental

L-TryptophanEvidence & Dosage

Serotonin/Melatonin, amino‑acid competition and outcomes.

Studies last updated

Evidence at a glance

Total studies
1,000
With abstract
50
Meta / Systematic / RCT
87
Highly cited
50
Publication years
1973–2026

L-Tryptophan in the context of Mental

This topic is part of our "Mental" world. There you'll find methodology, evidence and the highest-impact levers — plus the order in which they sensibly build on each other.

Go to Mental

Top studies on L-Tryptophan

Ranked by influential-citation count and publication year.

  1. The kynurenine pathway in major depressive disorder, bipolar disorder, and schizophrenia: a meta-analysis of 101 studies.

    Mol Psychiatry2021n=10,912Meta-Analysis185 influential citations

    The importance of tryptophan as a precursor for neuroactive compounds has long been acknowledged. The metabolism of tryptophan along the kynurenine pathway and its involvement in mental disorders is an emerging area in psychiatry. We…

    Finding: In this meta-analysis of 101 studies with 10,912 participants, tryptophan and kynurenine were decreased across major depressive disorder, bipolar disorder, and schizophrenia.

  2. An integrated meta-analysis of peripheral blood metabolites and biological functions in major depressive disorder.

    Mol Psychiatry2021n=49Meta-Analysis133 influential citations

    Major depressive disorder (MDD) is a serious mental illness, characterized by high morbidity, which has increased in recent decades. However, the molecular mechanisms underlying MDD remain unclear. Previous studies have identified altered…

    Finding: The meta-analysis identified 23 metabolites that differed significantly between MDD patients and controls across 46 studies.

  3. Exploring the Etiological Links behind Neurodegenerative Diseases: Inflammatory Cytokines and Bioactive Kynurenines.

    Int J Mol Sci2020n=22Systematic Review103 influential citations

    Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the most common neurodegenerative diseases (NDs), presenting a broad range of symptoms from motor dysfunctions to psychobehavioral manifestations. A common clinical course is the…

  4. Relationship Between the Gut Microbiome, Tryptophan-Derived Metabolites, and Osteoarthritis-Related Pain: A Systematic Review with Meta-Analysis.

    Nutrients2025n=756Meta-Analysis103 influential citations

    <h4>Introduction</h4>Osteoarthritis (OA) is the most prevalent form of arthritis and affects over 528 million people worldwide. Degenerative joint disease involves cartilage degradation, subchondral bone remodeling, and synovial…

    Finding: The meta-analysis found no significant association between the presence of pain in OA and the presence of bacilli of the genus Streptococcus or plasma markers of the tryptophan pathway.

  5. Therapeutic mechanisms of traditional Chinese medicine to improve metabolic diseases via the gut microbiota.

    Biomed Pharmacother2021Systematic Review97 influential citations

    Metabolic diseases such as obesity, type 2 diabetes mellitus, and hyperlipidemia are associated with the dysfunction of gut microbiota. Traditional Chinese medicines (TCMs) have shown considerable effects in the treatment of metabolic…

  6. Effect of immune activation on the kynurenine pathway and depression symptoms - A systematic review and meta-analysis.

    Neurosci Biobehav Rev2020n=315Meta-Analysis71 influential citations

    Dysregulated kynurenine (KYN) pathway has been implicated in the pathophysiology of depression. In this systematic review, we examined the relationship between kynurenine pathway metabolites (KYN, kynurenic acid KYNA, tryptophan TRP,…

    Finding: In this systematic review and meta-analysis, IFN-α treatment in patients with chronic illnesses was associated with decreased TRP, increased KYN, and increased KYN/TRP ratio.

  7. Brain Versus Blood: A Systematic Review on the Concordance Between Peripheral and Central Kynurenine Pathway Measures in Psychiatric Disorders.

    Front Immunol2021n=59Systematic Review70 influential citations

    Objective Disturbances in the kynurenine pathway have been implicated in the pathophysiology of psychotic and mood disorders, as well as several other psychiatric illnesses. It remains uncertain however to what extent metabolite levels…

  8. The kynurenine pathway in bipolar disorder: a meta-analysis on the peripheral blood levels of tryptophan and related metabolites.

    Mol Psychiatry2021n=16Meta-Analysis65 influential citations

    Growing evidence suggests that a dysregulation of the kynurenine pathway (KP) occurs in bipolar disorder (BD). This systematic review and meta-analysis aimed at assessing the possible differences in peripheral blood levels of KP…

  9. The tryptophan catabolite or kynurenine pathway in schizophrenia: meta-analysis reveals dissociations between central, serum, and plasma compartments.

    Mol Psychiatry2022n=281Meta-Analysis64 influential citations

    The tryptophan catabolite (TRYCAT) pathway is implicated in the pathophysiology of schizophrenia (SCZ) since the rate-limiting enzyme indoleamine-dioxygenase (IDO) may be induced by inflammatory and oxidative stress mediators. This…

    Finding: No significant increase was found in the neurotoxic composite score based on KYN, 3HK, and picolinic, xanthurenic, and quinolinic acid.

  10. The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression.

    Nutr Rev2022n=18meta63 influential citations

    CONTEXT: L-tryptophan (Trp) has been documented to aid sleep, but a systematic compilation of its effect on sleep quality is still limited. OBJECTIVE: We assessed the effect of Trp supplementation on sleep quality via meta-analysis and…

    Finding: Trp supplementation did not affect other sleep components.

Frequently asked

What does the evidence say about L-Tryptophan?
In this meta-analysis of 101 studies with 10,912 participants, tryptophan and kynurenine were decreased across major depressive disorder, bipolar disorder, and schizophrenia.
What dosage was studied?
• Assessment of kynurenine pathway metabolites (Not reported) • Peripheral blood metabolite profiling in MDD (meta-analysis of observed studies; no intervention) (not reported) • Not applicable; literature review of inflammatory cytokines and bioactive kynurenines (Not reported)
Are there safety considerations for L-Tryptophan?
• Not reported • IFN-α treatment was associated with increased depression scores. • IFN therapy can cause iatrogenic depression in up to 60% of patients. • Some studies allowed pain, fever, and nausea medications during treatment.

More topics in Mental

5-HTP

Serotonin precursor, mood, and Carbidopa safety.

Anxiety

Acute anxiety vs. an anxiety disorder, the neurobiology, interventions.

Ashwagandha (Stress)

Adaptogen — cortisol lowering, sleep, anxiety reduction.

Breathwork

Box breathing, 4-7-8, Wim Hof, pranayama — autonomic regulation.

Burnout Early Signs

Exhaustion, cynicism, dropping performance — spotting it before the crash.

Caffeine & Anxiety

Adenosine antagonism, individual sensitivity, cut-off strategies.

CBT

Cognitive behavioral therapy — the gold standard for anxiety and depression.

Co-Regulation

Nervous-system regulation within relationship — attachment, therapy, parent-child.

Cold Exposure (Mood)

Norepinephrine, depression, and mood effects of cold.

Depression

Symptoms, the monoamine hypothesis, lifestyle interventions, professional help.

Depth Psychology

Psychodynamic therapy, transference, long-term change.

Doomscrolling

Algorithm-driven negative info consumption — mood effects, limits.

EMDR / Trauma Therapy

PTSD, eye movements, and study effectiveness.

Exercise as Antidepressant

Aerobic exercise — efficacy comparable to SSRIs in mild depression.

Fight/Flight/Freeze

Stress-response patterns, somatic manifestation, regulation.

Glucose & Mood

Glucose swings, reactive hypoglycemia, mood stability.

Gut-Brain Axis

Vagus nerve, short-chain fatty acids, the microbiome's influence on mood.

Journaling (Mental)

Expressive writing, gratitude — reducing stress, anxiety and depression.

Lavender

Silexan studies, oral and olfactory — anxiolysis with a good safety profile.

Meditation

Mindfulness, concentration, loving-kindness meditation — effects and practice.

Related topics from other worlds

Performance

Deload

Planned recovery periods — avoiding overreaching.

Performance

HMB

Sarcopenia, Anti-Catabolic, and Sports Applications

Performance

Nitrate

Nitric oxide precursor, endurance performance, blood pressure lowering.

Performance

SARMs

Selective androgen receptor modulators — doping, off-label, liver risk.

Performance

VO2max Training

Intervals, VO2max, cardiovascular ceiling and protocols.

Recovery

Compression Recovery

Compression garments, lymphatic drainage, and recovery studies.