Supplement evidence
5-HTP
What the trials show, and the serotonergic interactions that make it a pharmacist question.
What Its Legal Status Actually Means
Read this before anything below it. Legal to sell is not the same fact as reviewed, verified, or approved.
5-HTP is sold in the US as a dietary supplement under DSHEA. It has never been approved by the FDA to treat depression, anxiety, insomnia, fibromyalgia, or anything else, and no FDA review of safety, purity, or effectiveness precedes it going on sale. Its close relative L-tryptophan was withdrawn from the US market in 1989-1990 after the eosinophilia-myalgia outbreak and later returned; 5-HTP, which is manufactured differently — usually extracted from the seed of the African plant Griffonia simplicifolia rather than produced by bacterial fermentation — was never part of that recall and has remained on sale throughout. Because it is a supplement, the amount of 5-HTP in a capsule and the presence of process contaminants are the manufacturer's responsibility, not a regulator's.
Quoted whole from the 2026-08-18 study harvest. Not summarized, not shortened.
What the Research Shows
4 records from the 2026-08-18 harvest, each checked against PubMed and Europe PMC on that date. How a study was designed, how many people were in it, and who paid for it are printed above what it found, because those three facts decide how much the finding is worth.
Study 1 · 2002
- Systematic review of randomized trials
- 64 participants
- Top-tier journal
- Funding not established
moderate69/100Reasonable evidence with real limitations.
Read this first: The pooled odds ratio looks impressive but rests on 64 patients with a confidence interval running from 1.28 to 13.15 — statistically positive and practically uninformative. The review is from 2002 and predates almost nothing, because almost nothing usable has been published since.
The reviewers located 108 trials of tryptophan or 5-HTP for depression and found that only two of them, involving 64 patients in total, were of sufficient quality to include. Those two favoured the supplements over placebo (Peto odds ratio 4.10, 95% CI 1.28 to 13.15), but the reviewers judged the evidence insufficient to be conclusive and concluded that, because antidepressants proven effective and safe already exist, the clinical usefulness of 5-HTP and tryptophan is limited. This remains the only Cochrane review of 5-HTP for depression and has not been updated in over two decades.
Shaw K, Turner J, Del Mar C. (2002). Tryptophan and 5-hydroxytryptophan for depression. Cochrane Database of Systematic Reviews. PMID 11869656.
How this record was checked
PubMed record 11869656 fetched via NCBI efetch 2026-08-18; title, authors, journal (Cochrane Database Syst Rev 2002;(1):CD003198), year, DOI, and the exact figures — 108 trials located, 2 included, 64 patients, Peto OR 4.10 (95% CI 1.28-13.15) — confirmed from the abstract. Europe PMC core record checked 2026-08-18: no grant list and no funding statement available, and the Cochrane Library page was not read, so funding is recorded UNKNOWN and conflicts false. A PubMed search on CD003198 returned no later version, so this 2002 review is the current one.
Study 2 · 2020
- Systematic review of observational studies
- Reputable journal
- Funding not established
- Preregistered
moderate63/100Reasonable evidence with real limitations.
Read this first: A pooled remission rate from mostly uncontrolled trials measures how many people improved, not how many improved because of 5-HTP; depression remits substantially on placebo and with time. Classified here as a systematic review of largely non-randomised evidence rather than a meta-analysis of RCTs for exactly that reason.
Thirteen studies entered the systematic review and seven the meta-analysis, yielding a pooled depression remission rate of 0.65 (95% CI 0.55 to 0.78) and a large effect on questionnaire scores (Hedges' g 1.11, 95% CI 0.53 to 1.69) with substantial heterogeneity (I-squared 76%). The authors' own risk-of-bias assessment rated the underlying studies as relatively weak, noting that few included placebo groups — which is why a 65% remission rate here is not comparable to a placebo-controlled remission rate, and why they call for placebo-controlled trials in well-defined patients.
How this record was checked
PubMed record 31504850 fetched via NCBI efetch 2026-08-18; title, all six authors, journal (Nutr Rev 2020;78(1):77-88), year, DOI, the 13-study/7-study split, remission rate 0.65 (95% CI 0.55-0.78), Hedges' g 1.11, and the PROSPERO registration CRD42018104415 (hence preregistered true) all confirmed from the abstract. Europe PMC core record checked 2026-08-18: no PMC full text, no grant list, no funding statement, so funding is recorded UNKNOWN and conflicts false. Total participant N is not stated in the record, so sampleSize is left null rather than guessed.
Study 3 · 2013
- Randomized trial
- 60 participants
- Reputable journal
- Funding not established
moderate57/100Reasonable evidence with real limitations.
Read this first: No placebo arm and no power calculation for equivalence: a trial in which both arms improve and neither wins cannot distinguish "both work" from "neither works and people recovered anyway", and 60 completers is far too few to establish non-inferiority. A single-centre trial that has not been replicated.
Seventy Indian patients in a first depressive episode were randomised to L-5-HTP or fluoxetine for eight weeks; 60 completed. Both groups improved on the Hamilton Depression Rating Scale from week two onward with no meaningful difference between them — 73.3% responded on 5-HTP versus 80% on fluoxetine — and the authors concluded the two were comparable. There was no placebo arm, so the trial shows only that the two treatments moved together, not that either beat the natural course of a first episode.
How this record was checked
PubMed record 23380314 fetched via NCBI efetch 2026-08-18; title, all five authors, journal (Asian J Psychiatr 2013;6(1):29-34), year, DOI, and the numbers — 70 recruited, 60 completed and randomised into two arms, 8 weeks, 73.33% versus 80% response — confirmed from the abstract. Europe PMC core record checked 2026-08-18: no PMC full text, no grant list, no funding statement, so funding is UNKNOWN, conflicts false, and independence left null (unchecked) rather than asserted.
Study 4 · 2025
- Randomized trial
- 30 participants
- Indexed journal
- Independently funded
- Preregistered
- Declared conflicts of interest
strong80/100Well-supported by good-quality research.
Read this first: The rubric score overstates this trial badly. It was single-blinded with a no-supplement control rather than a placebo capsule, so expectancy is uncontrolled; it enrolled 30 people; and the mood change it reports is half a point on a scale where the group started at 1.2 out of 15, which is not clinically interpretable as treating depression. It is included as the most recent randomised 5-HTP evidence that exists, which is itself the point: this is what "current evidence" looks like for 5-HTP.
Thirty Singaporean adults averaging 66 years old were randomised to 100 mg/day of 5-HTP or to no supplement for 12 weeks. The 5-HTP group's Montreal Cognitive Assessment score rose about one point (26.6 to 27.6) and its Geriatric Depression Scale score fell from 1.2 to 0.7, with serum serotonin rising; anxiety scores and the other blood biomarkers did not change. The authors themselves flag the small sample and short duration and call the results preliminary — and the baseline depression score of 1.2 on a 15-point scale means these were people with essentially no depression to treat.
How this record was checked
PubMed record 40944161 fetched via NCBI efetch 2026-08-18; title, all four authors, journal (Nutrients 2025;17(17):2773), year, DOI, N=30, the 100 mg/day dose, the 12-week design, and the MoCA and GDS figures confirmed from the abstract, which also carries "The authors declare no conflict of interest" (hence conflicts true). Europe PMC core record fetched 2026-08-18 lists National University of Singapore iHealthtech grants R-160-000-A89-133 and R-160-000-A89-733, hence funding INDEPENDENT. PMC full text PMC12430700 read 2026-08-18 confirms registration at ClinicalTrials.gov as NCT04078724, hence preregistered true, and confirms the single-blind, no-supplement-control design.
The Risks
Nobody checks this purchase the way a prescription is checked. No prescriber reviews it against the rest of what you take, no pharmacist screens the interaction, and no regulator confirms the dose in the capsule before it is sold. That is why this section sits here at full length rather than as a footnote.
What the paragraph below covers:
- Serotonin syndrome
- Drug interactions
- What is actually in the product
- Stomach and gut
- Sedation
5-HTP is a direct serotonin precursor, so the interaction that matters is with other serotonergic drugs: SSRIs, SNRIs, MAOIs, triptans, tramadol, linezolid, and St John's wort. Serotonin syndrome from 5-HTP is a theoretical and case-report-level concern rather than something demonstrated in controlled trials, but the mechanism is real and it is the single best reason to tell a prescriber before combining. The commonly reported side effects are nausea, vomiting, diarrhoea, and drowsiness. On the eosinophilia-myalgia question, the accurate version is this: the 1989 outbreak — 1,345 cases meeting the CDC surveillance case definition, with deaths — was traced to contaminated L-tryptophan produced by a single Japanese manufacturer, Showa Denko, and case-control studies found illness essentially confined to that manufacturer's product. It was not a 5-HTP outbreak. The related but distinct concern is that a trace contaminant nicknamed "peak X" has been reported in some 5-HTP samples and a small number of EMS-like cases have been described in 5-HTP users; no outbreak has ever been established, the analytical significance of peak X is disputed, and the dispute has never been settled by a regulator, because no regulator tests these products before sale.
What Is Not Known
The boundaries of the section above, in the harvest’s own words. What it excluded, why, and where it looked and found nothing. An absence of evidence is not evidence of absence, and it is not evidence of benefit either.
What Was Left Out, and Why
Quoted from the harvest, where these notes sat above the study list rather than after it. Where a note says “below” it means the studies in the section above.
- Das 2004 "Safety of 5-hydroxy-L-tryptophan" (Toxicol Lett, PMID 15068828) was fetched and verified but is excluded as a study record: it is a narrative safety review written from a supplement-industry laboratory (ISSI Laboratories Inc.) arguing that the "peak X" contaminant concern lacks credibility. It informed the known_risks wording only, and is flagged here so the reader knows a pro-supplement safety review exists and who wrote it.
- The 1989 eosinophilia-myalgia epidemiology (Kilbourne 1996 PMID 8895184; Sullivan 1996 PMID 8895159, 1,345 CDC-surveillance cases) was fetched to fix the facts in known_risks but concerns L-tryptophan, not 5-HTP, so it is not listed as a 5-HTP efficacy study.
- Pre-1990 open-label 5-HTP series are excluded; the Shaw Cochrane review rejected 106 of 108 located trials on quality grounds, and repeating them here would inflate the record.
The Retraction Check
PubMed efetch records for all four PMIDs inspected 2026-08-18 for "Retraction in" flags; none present, and no errata or expressions of concern.
Questions for a Prescriber or Pharmacist
This page does not tell anyone to take 5-HTP or to avoid it. It is not able to: it does not know what else you take, what you have tried, or what you are treating. These are the questions each study above raises, written to be asked out loud.
- Only two usable trials of 5-HTP for depression exist and they enrolled 64 people between them — is there any reason to bet on that instead of a treatment that has been tested in thousands?
- Most of the 5-HTP studies had no placebo group, so people got better but nobody knows against what — does that change how much weight we should put on the numbers?
- The one trial comparing 5-HTP to an antidepressant had 60 people finish and no placebo group — is that enough for you to consider it a real alternative to an SSRI?
- The newest 5-HTP trial had 30 people, no placebo pill, and participants who weren't depressed to begin with — does anything in it apply to someone who actually has depression?
And the one to ask at the counter, whatever the answers above turn out to be: given everything I am already taking, what would you want to know about 5-HTP before I put it in the same body?
Where This Page Comes From
Transcribed from the study-harvest-2026-08-18 record for 5-htp, built into this page by scripts/supplement-ingest.mjs on 2026-09-07. Nothing here is fetched at page load, and nothing here was written by a model without a citation behind it.
| Source file | study-harvest/2026-08-18/5-htp.yaml |
|---|---|
| Source repo | REPTechnologies/avalo-backend |
| SHA-256 | 00a378407387783000583e84ad975d34edd2f3a374c2474fb6207e6ecb8a7ccf |
| Also searched as | 5-HTP, 5-hydroxytryptophan, L-5-HTP, oxitriptan, Griffonia simplicifolia extract |
The Other Substances
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Do any supplements actually work? asks the question across all of them. The full library has the medication records, the funding investigations, and the glossary.