L-Tryptophan
EVIDENCE: MODERATEAlso sold as: tryptophan, L-Trp
Tryptophan is the essential amino acid the body uses to make serotonin and melatonin. A 2022 meta-analysis found 1 g a day or more may improve sleep quality. A 1989 outbreak of a serious illness was traced to contaminated batches from one manufacturer.
Compiled by iSupplementReviews editorial team ·Researched 2026-10-16 · 3 sources
- Type
- Essential amino acid
- Studied dose
- 1 g/day or more for sleep
- Best form
- pharmaceutical-grade L-tryptophan from a reputable source
- Our rating
- MODERATE — Several human trials — limits in size, duration, or independence
What is L-tryptophan?
L-tryptophan is an essential amino acid, meaning you must get it from food, and the body uses it to make serotonin and melatonin. It is sold for sleep and mood.
Other names and forms
Tryptophan, L-Trp. 5-HTP is a related compound one step closer to serotonin.
Where does L-tryptophan come from?
Protein foods such as poultry, eggs, cheese, fish and seeds. Typical diets supply roughly 1 g a day or more.
How does L-tryptophan work in the body?
The brain converts tryptophan into serotonin, which the pineal gland turns into melatonin. Tryptophan competes with other amino acids to enter the brain, so effects depend on dose and diet (Jenkins et al., 2016).
What is L-tryptophan claimed to do?
Improve sleep, mood and relaxation.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Sleep quality | Meta-analysis | ≥1 g/day | Modest positive |
| Mood in healthy people | Mixed experimental studies | Varied | Mixed |
| Blood sugar, hearing | None | — | Not studied |
Sleep
Doses of 1 g a day or more reduced time spent awake after falling asleep. Sutanto et al. (2022) pooled the trials; lower doses showed little effect.
The 1989 outbreak
Eosinophilia-myalgia syndrome sickened over a thousand people and was linked to contaminated tryptophan from one manufacturer. Ko et al. (2023) review the impurities identified and current safety concerns.
What dose was studied?
| Goal | Dose | Duration |
|---|---|---|
| Sleep | 1–5 g/day | Days to weeks |
Side effects
Drowsiness, nausea, dizziness.
Drug interactions
- SSRIs, SNRIs, MAO inhibitors, triptans, tramadol: serotonin syndrome risk (major).
- Sedatives: added drowsiness (moderate).
Who should not take L-tryptophan?
People on serotonin-affecting drugs, and those who are pregnant or breastfeeding without medical advice.
What the authorities say
FDA restricted L-tryptophan supplements after the 1989 outbreak and later allowed them back on the market. Product purity remains the main safety focus.
What to know about L-tryptophan
Tryptophan may modestly improve sleep at 1 g a day or more. Milligram amounts are far below what typical meals already provide.
Frequently asked questions about L-Tryptophan
Does tryptophan help sleep?
It may. A 2022 meta-analysis found doses of 1 g a day or more reduced time awake after falling asleep. Effects were modest.
Is tryptophan safe?
At normal doses, generally yes. In 1989 an illness called eosinophilia-myalgia syndrome was linked to contaminated tryptophan from one producer; impurities, not tryptophan itself, are the main suspected cause.
Can tryptophan interact with antidepressants?
Yes. Combined with SSRIs, MAO inhibitors or other serotonin drugs, it can raise the risk of serotonin syndrome. Ask your doctor first.
References
- [1]Sutanto CN et al. — The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression (Nutr Rev, 2022)
- [2]Jenkins TA et al. — Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis (Nutrients, 2016)
- [3]Ko SM et al. — Safety concerns regarding impurities in L-Tryptophan associated with eosinophilia myalgia syndrome (Food Chem Toxicol, 2023)
Products we reviewed containing L-Tryptophan
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.