An essential amino acid found in turkey, oats and seeds.
Why it’s used: The body uses it to make serotonin and melatonin.
L-tryptophan is an essential amino acid, which means the body cannot make it and it must come from food. It is found in protein-rich foods such as turkey, chicken, milk, cheese, oats, nuts and seeds, and most people get enough from a normal, varied diet.
The body uses tryptophan to make serotonin, a chemical messenger in the brain and gut, and melatonin, the hormone involved in the sleep-wake cycle. It can also be converted into niacin (vitamin B3). Researchers have studied tryptophan in relation to mood and sleep, but no health claims are authorised for it in the UK.
Tryptophan also has an important history. In 1989, an outbreak of a serious illness called eosinophilia-myalgia syndrome in the United States was linked to L-tryptophan supplements, and products were recalled. Investigators from the CDC and FDA later found contaminants in the batches linked to cases. This is why manufacturing quality and purity testing matter so much for tryptophan products. On labels it appears as L-tryptophan, with amounts in milligrams (mg).
3 findings behind this ingredient. Hover a card for the detail and the source.
Systematic review of 18 articles with a meta-analysis and meta-regression of 4. Tryptophan shortened wake after sleep onset, with a greater effect at 1 g a day or more; other sleep measures were unchanged.
Systematic review of 11 randomised controlled trials in healthy adults. Four showed significant effects on negative and happy feelings versus control, with doses of 0.14–3 g a day; no effect was seen on aggressive feelings.
Randomised double-blind study in 10 healthy volunteers given placebo, 1.2 g or 2.4 g L-tryptophan on separate days. Both doses shortened sleep latency at 1 hour, and the 2.4 g dose also at 2 hours.
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L-tryptophan is an essential amino acid that the body uses to make serotonin, melatonin and niacin. It comes from foods such as turkey, milk, oats and seeds. Researchers have studied it in relation to mood and sleep, but there are no authorised health claims.
Not without your doctor's advice. Tryptophan is a building block for serotonin, and combining it with SSRIs, SNRIs, MAOIs or other serotonergic medicines can cause serotonin syndrome, a potentially serious reaction. Speak to your GP or pharmacist first.
The 1989 eosinophilia-myalgia syndrome outbreak in the US was linked to L-tryptophan, and investigators found contaminants in the batches linked to cases. Choosing products made to good manufacturing standards with purity testing matters, and anyone with severe muscle pain or rash should seek medical advice.
Information only, not medical advice. If you take medication, are pregnant or breastfeeding, speak to your GP or pharmacist first.
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