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Tr8.0
Tryptophan Research
Likely helpsModerate safety
43 peer-reviewed studies
What the evidence says
Likely helps
Tryptophan appears to help in 5 of 6 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1982–2026 with a typical study size of 70 participants.
Based on 43 studies · 10 meta-analyses · 11 RCTs · 53,127 total participants
Confidence
High
What the studies found
5helped1unclear· 37 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
Osteoarthritis patients1
Active research area
35 studies in the last 5 years · Latest meta-analysis: 2025
198220042026
1Depressive disorder symptomsMeta-AnalysisCited 1×n=17,437 · very large study2025
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-AnalysisCited 23×n=4,647 · very large study2022
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.
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.
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.
7Association between serotonin and depressionSystematic ReviewCited 496×n=17 · very small study2023
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.
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.
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.
13Sleep and circadian disruption effects on microbiomeSystematic Review2026
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.
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.
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.
16Effectiveness of pharmacotherapy for sleep bruxismMeta-AnalysisCited 35×n=16 · very small study2014
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.
19Metabolomic profile modulation in sepsisRCTCited 10×n=210 · medium study2024
Findings suggest distinct metabolic dysregulation patterns associated with different immune dysfunctions in sepsis: the strongest metabolic dysregulation is associated with MALS.
Kranidioti E et al. · Critical care medicine (2024)
Findings suggest distinct metabolic dysregulation patterns associated with different immune dysfunctions in sepsis: the strongest metabolic dysregulation is associated with MALS.
20IBD-related fatigue reductionRCTCited 34×n=166 · medium study2022
Despite a significant increase in serum 5-hydroxytryptophan and serotonin levels, oral 5-hydroxytryptophan did not modulate IBD-related fatigue better than placebo. (Trial Registration: Belgian Federal Agency for Medication and Health Products, EudraCT number: 2017-005059-10 and ClinicalTrials.gov: NCT03574948, https://clinicaltrials.gov/ct2/show/NCT03574948.).
Truyens M et al. · Gastroenterology (2022)
No clear effect
← WorseNo effectBetter →
Could be chance
During 5-hydroxytryptophan treatment, a significant increase in serum 5-hydroxytryptophan (estimated mean difference, 52.66 ng/mL; 95% confidence interval [CI], 39.34-65.98 ng/mL; P < .001) and serotonin (3.0 ng/mL; 95 CI, 1.97-4.03 ng/mL; P < .001) levels was observed compared with placebo.
The proportion of patients reaching ≥20% reduction in fVAS was similar in placebo- (37.6%) and 5-hydroxytryptophan (35.6%)-treated patients (P = .830).