L-Tryptophan · supplement
Evidence tier: weak
A gentler upstream serotonin precursor than 5-HTP. Useful for sleep onset and mood support, especially when 5-HTP feels too sharp.
An essential amino acid and the raw material from which the body makes serotonin, and then melatonin. Supplying more of the precursor is presumed to raise serotonin availability and so improve sleep and mood. The precursor logic is sound biochemistry, but it does not deliver in practice: the pooled human sleep data show an effect on only one of four sleep measures, which is what a weak or absent downstream effect looks like. Precursor availability is not the rate limiting step it is marketed as.
Weak, and it carries the worst safety history of any ingredient in the modern supplement industry. On efficacy: the systematic review and meta analysis of tryptophan and sleep (PMID 33942088, Nutrition Reviews 2022) reviewed 18 articles but could pool only four, and found a single narrow effect. Tryptophan reduced wake after sleep onset, meaning time spent awake during the night, and did so only at doses of 1 g or more. It had NO meaningful effect on sleep latency, sleep efficiency or total sleep time. So it does not help you fall asleep and it does not lengthen your sleep; on four poolable trials it modestly reduces how long you lie awake in the middle of the night. Mood evidence is weaker still and rests on the serotonin precursor rationale rather than on convincing trials. Now the history, which is not optional context. In 1989 an outbreak of eosinophilia myalgia syndrome, a severe and sometimes irreversible illness, was traced to L-tryptophan from a single manufacturer, Showa Denko. More than 1,500 cases were reported to the CDC and at least 37 people DIED. The FDA recalled tryptophan in 1989 and banned most public sales in 1990; restrictions were loosened in 2001 and fully lifted in 2005. The causative contaminant has NEVER been definitively identified, which is precisely why the episode still matters: the failure was one of manufacturing purity, and the specific impurity that killed people was never pinned down, so the case for sourcing and purity discipline rests on an open question rather than a closed one. The other live risk is pharmacological: tryptophan raises serotonin, and taken with SSRIs or other serotonergic drugs it can precipitate serotonin syndrome, which is potentially life threatening.
The pooled sleep evidence only shows an effect at 1 g or more per day, and doses below 1 g performed materially worse. Any dose should be weighed against the purity history and against serotonergic drug interactions rather than chosen for effect alone.
500 to 1500 mg before bed, on an empty stomach (competes with other amino acids for transport).
CRITICAL interaction with SSRIs, MAOIs. Screen medications first.
Pregnancy: avoid
Breastfeeding: avoid
Active compounds: L-tryptophan
Remedies using L-Tryptophan · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.