1–3 g before bed.
At doses ≥1 g it somewhat shortens the time to fall asleep.
View the study (meta-analysis) →Mainly when there is a deficiency; scarce data.
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L-tryptophan is an essential amino acid (the body cannot synthesize it and it must be obtained from the diet) present in animal and plant proteins in modest but constant amounts; its biochemical singularity is that it is the sole precursor for the endogenous synthesis of serotonin and, through it, of melatonin, two neurotransmitter-hormones involved in the regulation of mood, sleep, appetite, and pain modulation; this central role as the limiting substrate of serotonergic synthesis explains its historical use as a supplement for depression, anxiety, and insomnia, an indication with moderate clinical support and a complex regulatory history.
Unlike 5-hydroxytryptophan (5-HTP), its intermediate metabolite in the synthetic pathway, tryptophan is a native nutrient present in the everyday diet, which makes it physiologically more conservative from a metabolic standpoint; the endogenous control system (the enzyme tryptophan hydroxylase) regulates conversion to 5-HTP according to brain serotonergic levels, whereas supplemental 5-HTP bypasses this regulatory control and can produce more erratic serotonergic levels, a relevant pharmacological difference.
The indication with the most solid clinical support is mild to moderate insomnia: several small studies and reviews have shown significant improvements in sleep latency and in the subjective quality of rest with doses of 1-3 grams taken 30-60 minutes before bedtime, an intervention consistent with conversion to nocturnal melatonin and with a tolerability profile more favorable than that of most pharmacological hypnotics.
Tryptophan was widely used as a natural hypnotic in the 1970s and 1980s until, in 1989, industrial contamination of a Japanese batch produced by the company Showa Denko caused an outbreak of eosinophilia-myalgia syndrome (EMS) affecting several thousand people and causing dozens of deaths; the problem was attributed to contaminants from the manufacturing process specific to one batch, not to tryptophan itself, but the episode led to its withdrawal from the market in many countries for years and to a commercial stigma that has only recently partially dissipated.
In mild to moderate depression, several small trials have shown significant improvements with doses of 3-6 grams per day for 4-8 weeks, especially in patients with a "serotonergic depression" profile (irritability, associated anxiety, sleep and appetite disturbances); the magnitude of the effect is modest compared with SSRIs and the clinical evidence is less solid than that for pharmacological antidepressants, so tryptophan is positioned as a complementary option or for mild cases where avoiding pharmacology is preferred.
In premenstrual syndrome with a predominant affective component, in bulimia nervosa, in seasonal affective disorder, and in tension headaches with a serotonergic hypoactivity profile, tryptophan has been used as an adjunctive intervention with moderate results; the physiological logic of supplementing the limiting substrate of serotonergic synthesis is sound and the clinical data are reasonable although heterogeneous.
The doses studied range from 500 milligrams to 6 grams per day; for insomnia, 1-3 g 30-60 minutes before bedtime, ideally with a little simple carbohydrate to favor brain uptake (tryptophan competes with the other large neutral amino acids for the transporter at the blood-brain barrier, and the insulin released by the carbohydrate lowers the plasma concentration of the competitors, favoring tryptophan entry); for depression, 3-6 g divided throughout the day.
The most frequent adverse effects are daytime drowsiness (if poorly dosed), nausea, and occasionally headache or vivid dreams; the most serious theoretical risk is serotonin syndrome if it is combined with SSRIs, SNRIs, MAOIs, triptans, tramadol, or other serotonergic drugs, an interaction that warrants caution and medical supervision; people with advanced liver cirrhosis or hepatic encephalopathy should avoid it because tryptophan can worsen the encephalopathy; in pregnancy and breastfeeding the data are limited and avoiding it is recommended; it is advisable to choose products with purity certification to minimize the theoretical risk of problematic contaminants similar to those in the historical 1989 episode.
Information, not medical advice. Scientific evidence reflects the quality of the studies.