L-tryptophan
Summary
L-tryptophan is an essential amino acid and the starting point for serotonin and melatonin. A pooled analysis found less time awake after falling asleep, mainly at 1 g or more, with no change in other sleep measures. Depression evidence is inconclusive. A contaminated batch caused the 1989 eosinophilia-myalgia outbreak.
Key facts
- An essential amino acid; precursor of serotonin, melatonin and niacin[2]
- Shorter wake time after sleep onset, mainly with ≥1 g; other sleep measures unchanged (pooled analysis of 4 studies)[1]
- Two adequate trials (64 people) favoured tryptophan or 5-HTP over placebo; evidence inconclusive[2]
- A 1989 epidemic of eosinophilia-myalgia syndrome was linked to contaminated L-tryptophan products[3]
- 1 graded human outcome on this page
- October 11, 2026
How it works
EstablishedTryptophan is converted to 5-HTP and then serotonin; serotonin is converted to melatonin in the pineal gland. Most tryptophan is used for protein and the kynurenine pathway, which makes niacin.[2][1]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Depressive symptoms | Improved | Grade D | Systematic review · n = 64 · 2001 People with unipolar depression or dysthymia in 2 trials Form: Tryptophan or 5-HTP · Dose: Varied across trials · Duration: Varied across trials Better than placebo (Peto OR 4.10) but only 2 of 108 trials met quality criteria; evidence was inconclusive. | 11687048 (opens PubMed)Source [2] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Free L-tryptophan tablets or capsules | Varies | No head-to-head human absorption data between products in the sources cited here. | The 1989 eosinophilia-myalgia outbreak was traced to contaminated products, not to tryptophan itself, according to the review cited here.[3] | Sleep and mood trials |
Studied doses
Doses studied in human trials ranged from under 1 g to 1 g or more; the pooled sleep analysis found the wake-time effect mainly at ≥1 g.[1]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Antidepressants and other serotonergic drugsReviewTryptophan raises serotonin production; combining it with drugs that raise serotonin adds to the effect.[4]
Other supplements
- 5-HTPReviewBoth feed the same serotonin pathway.[4]
Who should be careful
- People on antidepressants
- Serotonergic effects can add up; this belongs with the prescriber.[4]
- Product quality
- The 1989 outbreak came from contaminated supplements, so manufacturing quality matters.[3]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Where to buy L-tryptophan
Products from brands we partner with that contain L-tryptophan. Listing a product is not a claim that it works; check the amount per serving against the doses studied above, and the label for other ingredients.
- SupersmartPaid linkL-Tryptophan2 tablets: 1,000 mg L-tryptophan (500 mg per tablet); 60 servingsShop at Supersmart (opens in new tab)Price and label checked 2026-10-11 on the brand’s site.
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Frequently asked questions
Does tryptophan help sleep?
Pooled data suggest less time awake during the night at 1 g or more, but no change in other sleep measures.[1]
Is tryptophan the same as 5-HTP?
No. Tryptophan is converted to 5-HTP and then serotonin; 5-HTP skips the first, rate-limiting step.[2]
Is L-tryptophan safe after the 1989 outbreak?
The outbreak was traced to contaminated products; quality control is the lesson from that episode.[3]
Does turkey make people sleepy because of tryptophan?
Food protein supplies tryptophan alongside other amino acids; the trials cited here tested supplements, not meals.
Sources
- [1]The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression.. Nutr Rev, 2022. meta-analysis
- [2]Tryptophan and 5-hydroxytryptophan for depression.. Cochrane Database Syst Rev, 2001. systematic-review
- [3]L-tryptophan and the eosinophilia-myalgia syndrome: current understanding of the etiology and pathogenesis.. J Invest Dermatol, 1993. review
- [4]Safety of 5-hydroxy-L-tryptophan.. Toxicol Lett, 2004. review
What changed
- First draft. Every PMID checked against NCBI E-utilities (title, journal and year taken from the PubMed record) and each evidence row written from its PubMed abstract.