L-tryptophan is one of the nine essential amino acids, which the body cannot make and must get from food. As a supplement it is taken mainly for sleep.
Also known as: tryptophan, Trp.
A 2022 meta-analysis compared studies using less than 1 g a day with studies using 1 g a day or more (Sutanto 2022). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
What studies show: a 2022 review collected 18 articles and pooled 4 of them. Tryptophan shortened time spent awake after first falling asleep, more so at 1 g a day or more, but did not change other parts of sleep (Sutanto 2022). The pooled evidence is small.
Safety: in 1989 an outbreak of eosinophilia-myalgia syndrome (EMS), a rare illness with inflammation in muscles, skin, lungs and other organs, was tied to tryptophan supplements. A CDC-led investigation in Minnesota found that 29 of 30 patients whose source was known had taken tryptophan from a single manufacturer, compared with 21 of 35 healthy controls, and linked the cases to changes in that company's manufacturing (less purifying carbon and a new bacterial strain) (Belongia 1990). A 2023 review found that which impurity caused EMS is still not settled; several of its authors work for CJ CheilJedang, a tryptophan maker (Ko 2023). The sources here do not describe drug interactions.
We could not find a single published half-life or time to peak for L-tryptophan that applies to a supplement dose, so we do not list one.
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