L-Tryptophan
Also known as: Tryptophan, L-Tryp, 5-HTP precursor
The essential amino acid behind serotonin — evidence for sleep and mood, with a tragic 1989 contamination scandal in its history.
In short
L-tryptophan is an essential amino acid — the body cannot make it — that serves as the precursor to serotonin and melatonin. It must be obtained from food (turkey's reputation is mostly myth, but eggs, cheese, and seeds are genuinely rich) or supplements. Trials show modest benefits for sleep latency and sleep quality, and some support for mood in depression, though the evidence is mixed and effect sizes small. Its history carries a shadow: in 1989, contaminated tryptophan from one manufacturer caused the eosinophilia-myalgia syndrome outbreak that killed dozens and led to a US sales ban until 2005. The modern product is considered safe, but the episode remains a caution about supplement quality and the serotonin pathway's power.
- Essential amino acid; precursor to serotonin and melatonin
- 1989 EMS outbreak traced to one contaminated batch — 15-year US ban
- Modest trial support for sleep onset and quality
- Competes with other amino acids for brain uptake
What is L-Tryptophan?
L-tryptophan is the molecule your brain turns into serenity — biochemically speaking, it is the starting material for serotonin and melatonin, and supplementing it is one of the oldest mood-sleep interventions in the books. The clinical record is appropriately modest: small but real improvements in falling asleep and, historically, use as an antidepressant adjunct. But tryptophan also carries supplement history's most famous cautionary tale — the 1989 eosinophilia-myalgia outbreak that taught the industry what contaminated amino acids can do. The modern, tested product is safe; the story is worth knowing anyway.
Where it comes from
Natural sources
- Essential amino acid obtained from food: eggs, cheese, salmon, turkey, pumpkin seeds, oats
- Converted via tryptophan hydroxylase to 5-HTP, then serotonin, then melatonin
- Competes with other large neutral amino acids for blood-brain transport
How it's made
Produced by fermentation; sold as 500 mg–1 g capsules or powder.
What it does in products
Benefits
Sleep onset and quality
moderate evidenceTrials and meta-analyses find tryptophan at 1 g reduces time to fall asleep and improves subjective sleep quality, particularly in mild insomnia.
Mood support
moderate evidenceHistorically used as an antidepressant; modern reviews find modest effects, with some evidence as an adjunct and in seasonal affective disorder.
Premenstrual mood symptoms
emerging evidenceSeveral trials report reduced irritability and mood swings in late luteal phase.
Side effects & safety
Safety considerations
- Avoid supplemental use in pregnancy; insufficient safety data.
- SSRIs, SNRIs, MAOIs, and other serotonergic drugs — serotonin syndrome risk; avoid or strictly supervise
- Sedatives — additive drowsiness
- Not for: Concurrent serotonergic medication without medical supervision
- Not for: History of eosinophilia-myalgia syndrome
How it's used
In supplements
500 mg–1 g at bedtime for sleep; some mood trials used 3 g/day in divided doses. Take away from protein meals to improve brain uptake.
In skincare
Not a topical ingredient.
Regulatory status
- Sold as a dietary supplement (reallowed 2005); not FDA-approved for any condition.
- Not applicable.
Popular products containing L-Tryptophan
- NOW L-Tryptophan — 500 mg–1,000 mg capsulesNOW Foods · Supplement
- Doctor's Best L-Tryptophan — 500 mg veggie capsDoctor's Best · Supplement
- Life Extension Tryptophan — 1,000 mg tabletsLife Extension · Supplement
Product names and brands are shown for reference and belong to their respective owners.
The 1989 EMS outbreak
In 1989, a cluster of eosinophilia-myalgia syndrome cases — severe muscle pain, elevated eosinophils, organ damage, over 1,500 cases and 37 deaths — was traced to L-tryptophan from a single Japanese manufacturer whose process change introduced a toxic contaminant. The FDA banned tryptophan sales until 2005. The episode did not indict tryptophan itself but demonstrated that amino-acid manufacturing purity is a safety issue, and it permanently shaped quality standards.
Food vs supplement
Dietary tryptophan raises brain serotonin only weakly because it competes with other amino acids for transport — the famous 'turkey coma' is mostly post-meal blood-flow redistribution. Supplements (especially without protein) bypass the competition and deliver a stronger, measurable effect, which is why dosing advice emphasizes taking it away from meals.
Frequently asked questions
L-tryptophan or 5-HTP — which is better?
5-HTP skips the rate-limiting enzyme step and crosses the brain barrier more directly, but carries higher serotonin-syndrome risk with antidepressants. Tryptophan is the more conservative choice.
Can I take tryptophan with melatonin?
They act on the same pathway (tryptophan → serotonin → melatonin) and are often stacked at low doses; start with one and add cautiously.
Is tryptophan safe now?
Modern fermented tryptophan is manufactured under strict purity controls and is considered safe at standard doses for healthy adults.
The bottom line
L-tryptophan is a legitimate, modest sleep-and-mood amino acid whose modern safety is solid — provided it is never combined carelessly with serotonergic drugs.
References
- L-tryptophan and sleep: systematic review. PubMed Central. https://pubmed.ncbi.nlm.nih.gov/31092082/
- Tryptophan and depression. PubMed. https://pubmed.ncbi.nlm.nih.gov/27124122/
- Eosinophilia-myalgia syndrome — historical review. New England Journal of Medicine. https://pubmed.ncbi.nlm.nih.gov/1913640/