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Tr5.5
Tryptophan Research
Likely helps
151 peer-reviewed studies
What the evidence says
Likely helps
Tryptophan appears to help in 5 of 7 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1970–2026 with a typical study size of 70 participants.
Based on 151 studies · 12 meta-analyses · 106 RCTs · 25,345 total participants
Confidence
High confidence
What the studies found
5helped2unclear· 144 more without graded effect data
By outcome
Depression & moodImproved mood through serotonin support · 1-2 weeks
Patients with major depressive disorder with melancholic and psychotic features1
Bipolar disorder patients1
Active research area
54 studies in the last 5 years · Latest meta-analysis: 2026
197019982026
1Depressive disorder symptom improvementMeta-Analysisn=17,437 · very large study2025
In plain English: This extensive systematic review and NMA of nutraceuticals for treating depressive disorders indicated a number of nutraceuticals that could offer benefits, either as adjuncts or monotherapies.
Cheng YC et al. · Psychological medicine (2025)
Adjunctive nutraceuticals consistently showed better efficacy than antidepressants (ADT) alone in outcomes including SMD, remission, and response.
This extensive systematic review and NMA of nutraceuticals for treating depressive disorders indicated a number of nutraceuticals that could offer benefits, either as adjuncts or monotherapies.
2Tryptophan and metabolite levels in severe depressionMeta-Analysisn=4,647 · very large study2022
In plain English: Patients with affective disorders with melancholic and psychotic features and suicidal behaviors showed normal IDO enzyme activity but a lowered availability of plasma/serum TRP to the brain, which is probably due to other processes such as low albumin levels.
Almulla AF et al. · Cells (2022)
Large benefit
← WorseNo effectBetter →
Likely real
Severe patients showed significant lower (p < 0.0001) TRP (standardized mean difference, SMD = -0.517, 95% confidence interval, CI: -0.735; -0.299) and TRP/CAAs (SMD = -0.617, CI: -0.957; -0.277) levels with moderate effect sizes, while no significant difference in CAAs were found.
Kynurenine (KYN) levels were unaltered in severe MDD/BD phenotypes, while the KYN/TRP ratio showed a significant increase only in patients with psychotic features (SMD = 0.224, CI: 0.012; 0.436).
Quinolinic acid (QA) was significantly increased (SMD = 0.358, CI: 0.015; 0.701) and kynurenic acid (KA) significantly decreased (SMD = -0.260, CI: -0.487; -0.034) in severe MDD/BD.
In plain English: At least 13 studied genes with polymorphisms were involved in MDD development according to MF and BP, but not significantly.
Suktas A et al. · BMC psychiatry (2024)
A similar result was observed for BDNF rs6265 GG (OR = 1.26; 95% CI = 0.78-2.06; P = 0.35) and BDNF rs6265 AA genotypes (OR = 1.12; 95% CI = 0.77-1.64; P = 0.56).
At least 13 studied genes with polymorphisms were involved in MDD development according to MF and BP, but not significantly.
These results suggest that MDD development risk factors might require genetic and other factors for interaction and induction.
In plain English: The TRYCAT pathway appears to be downregulated in BD patients.
Hebbrecht K et al. · Frontiers in immunology (2021)
Noticeable benefit
← WorseNo effectBetter →
Likely real
Peripheral levels of tryptophan (SMD = -0.44; p < 0.001), kynurenine (SMD = - 0.3; p = 0.001) and kynurenic acid (SMD = -.45; p = < 0.001) were lower in BD patients versus healthy controls.
The TRYCAT pathway appears to be downregulated in BD patients.
There is a need for more and high-quality studies of peripheral and central TRYCAT levels, preferably using longitudinal designs.
9Association between serotonin and depressionSystematic Reviewn=17 · very small study2023
In plain English: This meta-analysis examined the effects of Tryptophan.
Moncrieff J et al. · Molecular psychiatry (2023)
The main areas of serotonin research provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations.
Some evidence was consistent with the possibility that long-term antidepressant use reduces serotonin concentration.
In plain English: Well-designed, perimenopause-specific clinical trials are needed to confirm efficacy and inform microbiome-based nutritional strategies.
Conclusions: Gut microbiota dysbiosis may contribute to anxiety vulnerability in perimenopausal women through interconnected immune, metabolic, and neuroendocrine mechanisms.
Dietary modulation of the intestinal microbiota represents a biologically plausible and low-risk complementary approach to support emotional well-being during this transitional period.
11Sleep and circadian disruption effects on microbiomeReview2026
In plain English: We highlight directions for future mechanistic research, particularly in translational models, to clarify causal pathways and support microbiome-informed strategies for mitigating the health consequences of sleep and circadian disruption.Published by Elsevier Ltd.
Maki KA et al. · Neuroscience and biobehavioral reviews (2026)
Across studies, consistent links emerged between sleep and circadian disruption and changes in host homeostasis through microbiome-mediated mechanisms.
These include activation of the hypothalamic-pituitary-adrenal axis, altered bile acid metabolism, inflammation-related microbial shifts, and disrupted tryptophan pathways.
Together, these findings suggest that altered sleep influences metabolic and immune function via gut microbial signaling pathways.
12Sleep quality improvementMeta-Analysisn=28 · very small study2025
In plain English: Conclusions These findings suggest that tryptophan, vitamin D, omega-3, zinc, and antioxidants may enhance sleep quality by decreasing SL, and WASO increases SE and extends TST, respectively.
Mei M, Zhou Q, Gu W, Li F, Yang R, Lei H, Liu C. · Nutrients (2025)
No clear effect
← WorseNo effectBetter →
Borderline
NASO showed a marginal reduction (MD: -1.57, 95% CI: -3.16 to 0.02, p = 0.05).
Results This study, in total, included 28 randomized controlled trials.
Conclusions These findings suggest that tryptophan, vitamin D, omega-3, zinc, and antioxidants may enhance sleep quality by decreasing SL, and WASO increases SE and extends TST, respectively.
14Effectiveness of pharmacotherapy for sleep bruxismMeta-Analysisn=16 · very small study2014
In plain English: There was insufficient evidence on the effectiveness of pharmacotherapy for the treatment of sleep bruxism.
Macedo CR et al. · The Cochrane database of systematic reviews (2014)
There was insufficient evidence on the effectiveness of pharmacotherapy for the treatment of sleep bruxism.
This systematic review points to the need for more, well-designed, RCTs with larger sample sizes and adequate methods of allocation, outcome assessment and duration of follow-up.
Ideally, parallel RCTs should be used in future studies to avoid the bias associated with cross-over studies.
In plain English: The goal for clinical research is to explore options for TRP-targeted therapies and their integration into new therapeutic strategies.
Holeček M · Nutrients (2026)
The final sections are devoted to the benefits and adverse effects of TRP supplementation, the therapeutic use of various TRP metabolites, and the pharmacological targeting of enzymes, transporters, and receptors involved in TRP catabolism.
It is concluded that all pathways of TRP catabolism are altered across a broad spectrum of human illnesses, and further investigation is needed to understand their role in disease pathogenesis better.
The goal for clinical research is to explore options for TRP-targeted therapies and their integration into new therapeutic strategies.
In plain English: The KP may play a key role in the pathophysiology of CS-associated behaviors, and could serve to highlight potential targets for novel therapeutic strategies, specifically for treatment resistance.
de Bartolomeis A, Fornaro M, Scopetta E, Ricci C, Irano A, De Simone G, Comai S, Iasevoli F, Caiazza C. · European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology (2025)
We performed a systematic review and meta-analysis following a pre-determined protocol (PROSPERO:CRD42023459414), considering KP metabolites and enzymes as outcomes (Standardized Mean Difference=SMD).
CS proved to increase hippocampal and cortical overall concentrations of kynurenine (SMD=1.71,95 %C.I.[0.99,2.42], p < 0.01,I 2 =91.3 %,k = 23,n = 508; SMD=1.54,95 %C.I.[1.08,2.01],p < 0.01,I 2 =57.77 %,k = 16,n = 247), as well as kynurenine/tryptophan ratio and quinolinic acid.
KP enzyme expression/activity, including Indoleamine-2,3-Dioxygenase, Tryptophan-2,3-Dioxygenase, Kynurenine-3-Monoxygenase, increased.
In plain English: This systematic-review examined the effects of Tryptophan.
Zhang Y et al. · Cell communication and signaling : CCS (2026)
Finally, we propose a conceptual "diet-microbiota-drug" triad to guide precision interventions, and discuss current challenges such as interindividual variability, the lack of standardized assessment tools, and the need for integrative multi‑omics and clinical validation.
A deeper mechanistic understanding of gut-organ crosstalk may pave the way for innovative therapies to restore systemic metabolic homeostasis.
In plain English: Broader application of this research could ultimately refine personalized psychiatry, expand therapeutic horizons, and contribute to global mental health resilience.
Chehadi AC et al. · International journal of molecular sciences (2026)
Special emphasis is placed on translational potential, methodological limitations, and the need for harmonized research frameworks.
Here we highlight that phytochemical interventions represent a mechanistically informed and biocompatible strategy for advancing depression management.
By bridging neurobiology and clinical psychiatry, these insights may pave the way for next-generation therapeutics that integrate dietary, microbiota-targeted, and anti-inflammatory approaches.
In plain English: However, these findings should be interpreted cautiously due to substantial heterogeneity and limited control for key confounders such as antipsychotic medication, diet, and life-style factors.
Militaru AM, Pietreanu AC, Trifu S, Popa GL. · International journal of molecular sciences (2026)
Meta-analyses revealed no statistically significant differences in alpha diversity indices (Shannon, Simpson, Chao1, ACE, Observed) between patients and controls, despite high heterogeneity.
Taxonomic synthesis identified recurrent but heterogeneous dysbiotic patterns characterized by the depletion of short-chain fatty acid-producing taxa (e.g., Faecalibacterium , Roseburia , Lachnospiraceae) and enrichment of pro-inflammatory taxa (e.g., Proteobacteria, Fusobacterium ).
Schizophrenia is associated with evidence of compositional alterations and functional shifts rather than a global loss of microbial richness.