5-HTP and L-Tryptophan: Independent Evidence on Mood, Sleep, Risk

Table of contents

• Evidence summary
• What 5-HTP and L-tryptophan are
• How they work
• What works and what does not
• Benefits by claim
• Risks and all side effects
• All interactions
• Who should avoid 5-HTP and L-tryptophan
• Doses studied and product quality
• Follow the money: who makes it and who funded the evidence
• Related research
• Frequently asked questions
• Sources and funding notes

Evidence summary

Independent evidence and credibility scorecard

Independence tiers: 1 = regulator or government body; 2 = academic or Cochrane team with no declared commercial funding for the work; 3 = independent authors analysing mostly manufacturer-run trials, or minor declared industry ties; 4 = manufacturer-funded or manufacturer-authored. Credibility runs from A (highest) to D.

Six of the twelve sources are from the US, and most of the contamination science comes from a small number of US teams. No tier 4 trial appears because we found no manufacturer-funded 5-HTP trial worth grading; the one tier 4 source is a regulator-approved product label.

What 5-HTP and L-tryptophan are

• L-tryptophan is one of the essential amino acids, found in protein foods. A Canadian product monograph describes L-tryptophan as an essential amino acid found in protein foods (pms-Tryptophan monograph). Manufactured tryptophan is made by bacterial fermentation (FDA 2001; Belongia et al. 1990).
• 5-HTP (5-hydroxy-L-tryptophan, L-5-HTP, oxitriptan) is made in the body from tryptophan. Many supplements are made from Griffonia simplicifolia seed extract (Cunningham et al. 2021). We did not check the manufacturing split.

Legal status by country

How they work

The pathway is simple on paper. Tryptophan is converted to 5-HTP, and 5-HTP is converted to serotonin (and, at night, melatonin). Taking 5-HTP skips that first step: it is the immediate precursor of serotonin (Das et al. 2004).

What is shown in humans: oral 5-HTP raises blood 5-HTP and serotonin. In the Belgian trial, serum 5-HTP and serotonin rose significantly during active treatment (Truyens et al. 2022).

What is not shown: that pushing more serotonin precursor into the body relieves depression. That idea rests on the "low serotonin" theory, which is itself disputed. A 2022 umbrella review concluded there is no consistent evidence linking depression to lowered serotonin (Moncrieff et al. 2022). We did not check that review's funding or declared interests. For sleep, NCCIH says it is unclear how tryptophan and 5-HTP work (NCCIH).

Some 5-HTP is converted to serotonin outside the brain. Research protocols have sometimes paired it with carbidopa, a peripheral decarboxylase inhibitor that blocks this conversion (Maffei 2020). The same combination has caused harm (see below).

What works and what does not

Benefits by claim

Depression

The Cochrane review by Kelly Shaw, Jane Turner and Chris Del Mar located 108 trials. Only two trials, with 64 patients, met its standard: randomised, placebo-controlled, in unipolar depression or dysthymia (abstract). The two trials are not named in the abstract or the Cochrane summary we could open, so we cannot say which trials they are.

Pooled, more people responded on the supplements (Peto odds ratio 4.10, 95% CI 1.28 to 13.15). In plain terms, the odds of responding were about four times higher, and roughly one extra person responded for every three treated (NNT 2.78). But the confidence interval is very wide, the responder analysis covered only 46 people, and the reviewers judged the evidence too poor to be conclusive. They added that, because proven antidepressants exist, the clinical usefulness of 5-HTP and tryptophan is "limited at present" (Cochrane 2002). A companion journal paper warned that the many poorly run studies raise the possibility of publication bias (Shaw et al. 2002).

The 2020 review by Florian Javelle and colleagues took a broader approach, including uncontrolled studies. Its remission estimate pooled 13 studies (0.65, 95% CI 0.55 to 0.78), and a questionnaire analysis of 7 studies gave a large improvement (Hedges' g 1.11). It also reported few placebo groups and generally low study quality (Javelle et al. 2020). Without placebo groups, a large before-and-after improvement cannot be separated from natural recovery and expectation.

Newer trials are small. An Indian trial found similar response rates for 5-HTP and fluoxetine over 8 weeks, with no placebo arm (Jangid et al. 2013). An Italian crossover trial in 25 people with Parkinson's disease found 50 mg a day improved depressive symptoms (Meloni et al. 2020).

L-tryptophan as a prescription add-on

In the UK, L-tryptophan is licensed only for treatment-resistant depression, after standard antidepressants have been tried, and only as an add-on (Optimax SmPC). Canada licenses it as an adjunct to antidepressant treatment, and other Canadian tryptophan monographs warn that some antidepressants and neuroleptics can increase sedation (Apo-Tryptophan monograph). Neither label we could read cites recent controlled trials, and we found none.

Anxiety and panic

In a Dutch trial of 45 people with anxiety disorders, clomipramine improved all rating scales, while 5-HTP gave a "moderate" reduction on two scales and did not help associated depressive symptoms (Kahn et al. 1987). A single 200 mg dose reduced panic provoked by breathing 35% carbon dioxide in 24 people with panic disorder, but not in healthy volunteers (Schruers et al. 2002). That is a laboratory model, not evidence of everyday benefit.

Sleep

A 2022 meta-analysis pooled only 4 tryptophan studies. Tryptophan shortened time awake after first falling asleep (SMD −1.08, 95% CI −1.89 to −0.28), but did not change other sleep measures (Sutanto et al. 2022). The American Academy of Sleep Medicine made a weak recommendation against tryptophan for chronic insomnia. The guideline summary says it rests on trials of 250 mg tryptophan (AASM 2017).

For 5-HTP, a Singapore trial gave 30 older adults 100 mg a day for 12 weeks. Poor sleepers taking 5-HTP improved their sleep-quality score (Sutanto et al. 2024). The control group took no supplement rather than a placebo pill, and the trial was single-blinded, so expectation could explain part of the result.

Fibromyalgia, migraine and weight

Health Canada allows 5-HTP labels to claim relief of fibromyalgia symptoms, migraine prevention and help with weight management, (Health Canada). The fibromyalgia evidence includes one 50-patient placebo-controlled trial whose authors called for further studies (Caruso et al. 1990). We did not check EU health-claim opinions on 5-HTP for this article.

Risks and all side effects

Common side effects

We could not check the Cochrane trials' side-effect counts against the full text (Cochrane full text). The Belgian trial gave 100 mg twice daily in two 8-week periods. We could not open its supplementary safety table to check the figures, so we do not quote them here (Truyens et al. 2022).

The UK label for L-tryptophan lists nausea (usually settling in 2 or 3 days and reduced by taking it after food), headache, light-headedness, drowsiness, oedema, fatigue and muscle pain (Optimax SmPC).

Mood worsening

The UK label reports suicidal thoughts and behaviour, of unknown frequency, during L-tryptophan treatment or soon after stopping, and asks for close monitoring early in treatment (Optimax SmPC).

All interactions

Who should avoid 5-HTP and L-tryptophan

• Anyone on serotonergic medicines, including antidepressants, triptans, tramadol and MAOIs, unless a prescriber has planned it (see interactions).
• Pregnancy and breastfeeding: there are no clinical data in pregnancy; the UK label advises caution in pregnancy and says not to take it while breastfeeding (Optimax SmPC). We could not confirm Health Canada's pregnancy wording in this check.
• Children: safety and efficacy have not been established (Optimax SmPC).
• People with scleroderma, or a past history of EMS (Health Canada; Optimax SmPC).
• Bipolar disorder: we did not confirm a bipolar-specific warning in the Canadian monograph. Anyone with bipolar disorder should ask their psychiatrist before use.
• Older adults and liver or kidney disease: the UK label suggests a lower dose may be appropriate (Optimax SmPC).
• Before surgery: tell the surgical team. Some drugs used around surgery, such as fentanyl and methylene blue, are on the serotonin-interaction lists above.

Doses studied and product quality

These are doses used in trials or written on official labels and monographs. They are not a recommendation to take either product.

Product quality and contamination

In 1998, Mayo Clinic researchers raised concerns about over-the-counter 5-HTP products (Williamson et al. 1998). US supplements do not need FDA approval before sale, and firms do not have to give the FDA their safety evidence (FDA). We found no recent independent testing of 5-HTP products for peak X.

Follow the money: who makes it and who funded the evidence

Who makes and sells it

• Raw material: Griffonia simplicifolia is a wild West African plant, and its seed supply is studied for sustainability. We did not check the trade figures in the paper (Cunningham et al. 2021). The authors review the challenges facing sustainable harvest.
• Market: we could not verify the size of the 5-HTP or Griffonia extract market from an official source, so we do not quote trade estimates.
• Prescription L-tryptophan: in the UK, Optimax is licensed to Esteve Pharmaceuticals Ltd (Optimax SmPC). In Canada, makers include Apotex (Apo-Tryptophan) and Pharmascience (pms-Tryptophan). Both are long-established, naturally occurring substances, and in our assessment no company has a strong commercial reason to fund large trials.

Who funded the evidence

• Cochrane 2002: we could not verify its sources-of-support or declarations statements (Cochrane full text). We could not find who funded the two included trials.
• Javelle 2020: no funding sources or sponsors (PROSPERO). We could not open the full text to check author declarations, the journal's sponsorship or the author affiliations.
• Recent trials: National University of Singapore grants (Li et al. 2025); a Belgian trial whose funding we could not verify (Truyens et al. 2022). We found no recent trial funded by a 5-HTP seller.
• The safety reassurance: NCCIH's purity wording is close to Das et al.'s, but we could not confirm it relies on that paper (NCCIH). The Das paper has an author at ISSI Laboratories Inc., a commercial laboratory, and argues that the peak X finding lacked credibility (Das et al. 2004). We could not see its funding statement. Mayo Clinic's structural work disagrees, identifying peak X as a putative neurotoxin (Klarskov et al. 2003).

Documented integrity events

• 1989, the EMS epidemic: Hill et al. describe several thousand cases and 36 deaths (Hill et al. 1993), and the FDA counts more than 1,500 reported cases and at least 37 deaths (FDA 2001).
• The source: in Minnesota, 29 of 30 patients with a known source had taken tryptophan from one company, against 21 of 35 controls (odds ratio 19.3). Affected lots were linked to less powdered carbon in purification and a new bacterial strain (Belongia et al. 1990). CDC investigators named the manufacturer as Showa Denko K.K. and found more than 60 trace contaminants, six of them associated with EMS (Hill et al. 1993; Kilbourne et al. 1996). Mayo Clinic researchers called it "a cautionary tale" for biotechnology products (Mayeno & Gleich 1994).
• Litigation: most claims were settled confidentially. Quackwatch reported that, according to the chair of the plaintiffs' steering committee, about 2,000 people sued or negotiated claims, and stated that Showa Denko's payments approximated US$1 billion (Quackwatch). We could not verify that total. On 1 January 2023 Showa Denko K.K. and Showa Denko Materials merged into two new companies, Resonac Holdings Corporation and Resonac Corporation (Resonac).
• 5-HTP: NIH clinicians described an EMS-like illness in a family exposed to 5-HTP containing an impurity; eosinophilia resolved in two family members after switching to a clean product (Michelson et al. 1994).

What this means: Unusually for a supplement, none of the recent evidence we traced was paid for by sellers, although the funding of most older trials is unknown. The bigger problem is scarcity: the trials are small, old and rarely placebo-controlled, and few companies have an incentive to pay for a large one. The safety evidence, by contrast, comes largely from public-health investigations.

Related research

For wider, evidence-graded context, see these Pure City Research guides:

• Stress, anxiety and depression supplements: evidence and safety
• Sleep supplements: evidence limits, product quality and safety
• St John's wort: depression evidence and serious interaction risks
• Saffron for depression
• Melatonin
• Glycine for sleep
• L-theanine
• Major depressive disorder
• Treatment-resistant depression
• Insomnia
• Sertraline (interacts with tryptophan)

Frequently asked questions

Sources and funding notes

What we could not verify: the Cochrane review's sources of support and declarations, and the names of its two included trials (the Cochrane Library blocked our access, and the abstract does not name them); the funding of most pre-2000 5-HTP trials; the funding of Truyens et al. 2022 (full text blocked); the Truyens safety table; the full text and author declarations of Javelle et al. 2020 (paywalled; we confirmed only its PROSPERO funding statement); the funding of Das et al. 2004; the EU status of 5-HTP and Griffonia extracts (the Commission catalogue would not open, so that status rests on secondary sources); the total value of EMS settlements; the Canadian Apo-Tryptophan monograph text (we read only a search summary of its indication and revision date, and could not read its interaction or bipolar wording); the Australian scheduling status; the Cunningham 2021 trade figures; the Belongia 1990, Hill 1993 and Kilbourne 1996 figures beyond their abstracts; the Kikuchi 2021 review; and any official figure for the size of the 5-HTP market. The archived FDA 2001 paper would not open in our check, so its EMS figures were confirmed through a copy hosted by the National EMS Information Network (NEMSN). Quackwatch gives a different death count (28); we did not resolve that difference. MedlinePlus pages for 5-HTP and L-tryptophan are no longer available.

1. Shaw K, Turner J, Del Mar C. Tryptophan and 5-hydroxytryptophan for depression. Cochrane 2002 (full text; summary) — main systematic review; funding and declarations not verified in this check.
2. Shaw K et al. Aust N Z J Psychiatry 2002 — journal version of the review; funding not checked.
3. Javelle F et al. Nutrition Reviews 2020 and PROSPERO CRD42018104415 — meta-analysis; no funding sources or sponsors.
4. Thomson J et al. Psychol Med 1982 — L-tryptophan trial (115 patients); not confirmed as a Cochrane-included trial; funding not stated in abstract.
5. Jangid P et al. Asian J Psychiatr 2013 — 5-HTP vs fluoxetine; funding not stated in abstract.
6. Meloni M et al. Eur J Neurol 2020 — Parkinson's depression trial; University of Cagliari; funding not seen.
7. Truyens M et al. Gastroenterology 2022 (full text) — placebo-controlled trial; funding and conflicts not verified (full text blocked).
8. Sutanto CN et al. Clin Nutr 2024 and NCT04078724 — sleep trial; National University of Singapore.
9. Li S et al. Nutrients 2025 — 2025 mood and cognition analysis from the same group; funding not re-checked.
10. Sutanto CN et al. Nutrition Reviews 2022 — tryptophan and sleep meta-analysis; National University of Singapore.
11. Kikuchi AM et al. J Diet Suppl 2021 (publisher page) — tryptophan and mood review; funding and declarations not checked.
12. Kahn RS et al. Int Clin Psychopharmacol 1987 — anxiety trial; Utrecht University Hospital; funding not stated.
13. Schruers K et al. Psychiatry Res 2002 — panic challenge study; Maastricht University; funding not stated.
14. Caruso et al. J Int Med Res 1990 — fibromyalgia trial; funding not stated.
15. Sateia MJ et al. AASM insomnia guideline 2017 — professional guideline; AASM; disclosure list not fully checked.
16. NCCIH: Sleep disorders and complementary health approaches (May 2024) — US government.
17. Moncrieff J et al. Mol Psychiatry 2023 (online 2022) — serotonin theory review; funding and declarations not checked.
18. Maffei, Int J Mol Sci 2020 — narrative review of 5-HTP sources and pharmacology; University of Turin local grants; no conflict declared.
19. FDA CFSAN. Information paper on L-tryptophan and 5-hydroxy-L-tryptophan (February 2001; archived copy) — US regulator.
20. FDA: Questions and answers on dietary supplements — US regulator.
21. CDC MMWR 1989 and CDC MMWR 1990 — outbreak surveillance; US government.
22. Belongia EA et al. NEJM 1990 — Minnesota case-control study; CDC and state health authors.
23. Slutsker L et al. JAMA 1990 — EMS linked to one manufacturer; authors and funding not checked.
24. Hill RH et al. 1993 and Kilbourne EM et al. 1996 — contaminant analysis and causation review naming Showa Denko; CDC authors.
25. Mayeno AN, Gleich GJ. Trends Biotechnol 1994 — manufacturing analysis; Mayo Clinic.
26. Allen JA et al. Arthritis Rheum 2011 — post-epidemic case; affiliations not checked.
27. Michelson D et al. J Rheumatol 1994 — 5-HTP EMS-like illness evaluated at NIH.
28. Mayo Clinic news release, August 1998, Williamson BL et al. Nat Med 1998 and Klarskov K et al. J Rheumatol 2003 — peak X findings; Mayo Clinic; funding not seen.
29. Das YT et al. Toxicol Lett 2004 — counter-view on peak X; one author at ISSI Laboratories Inc.; funding not seen.
30. Sternberg EM et al. NEJM 1980 — 5-HTP plus carbidopa case.
31. Zoloft (sertraline) prescribing information, Viatris — FDA-approved label.
32. Nardil (phenelzine) prescribing information, Pfizer — FDA-approved label.
33. Optimax 500 mg capsules SmPC — MHRA-approved; licence holder Esteve Pharmaceuticals Ltd; last updated 2 January 2026.
34. Health Canada 5-HTP monograph (2024) — Government of Canada.
35. Apo-Tryptophan product monograph (Apotex, revised March 2026) and pms-Tryptophan product monograph (Pharmascience, 2016) — Health Canada-authorised labels.
36. Australian Poisons Standard, June 2026 and Permissible Ingredients Determination (No. 2) 2026 — Australian government.
37. EU Novel Food Catalogue — European Commission; entries for 5-hydroxytryptophan and Griffonia simplicifolia (not opened; see gaps).
38. EFSA 2011, L-tryptophan claims and EFSA 2011, 5-HTP satiety claim — EU food safety agency.
39. Verbraucherzentrale: 5-HTP from the African black bean (June 2024) — German consumer advice centres, publicly funded.
40. MedlinePlus herbs and supplements index — US National Library of Medicine.
41. Cunningham AB et al. J Ethnopharmacol 2021 — Griffonia supply chain; funding statement not seen.
42. NutraIngredients, July 2021 — trade press.
43. Quackwatch: Notes on the tryptophan disaster — independent consumer website; litigation estimate unverified.
44. Resonac corporate profile — company website (Showa Denko successor).

Educational research reviewed 6 October 2026. This article is not medical advice; talk to a qualified clinician or pharmacist before starting, stopping or combining treatments.