Does tryptophan help with sleep problems and low mood?
Tryptophan at a dose of at least 1 gram per day demonstrably helps reduce time spent lying awake at night, and in healthy people it may also give mood a modest lift. For sleep quality overall, or for depression as a condition, the effect is too limited or too inconsistent to rely on.
Tryptophan has the most clearly measurable benefit for one specific sleep problem: lying awake after you have already fallen asleep. At a dose of at least 1 gram per day, people lay awake for an average of nearly 29 minutes less, compared with just over 56 minutes at a lower dose. No demonstrable effect has been found on other aspects of sleep, such as total sleep duration or the amount of deep sleep.
For mood, a summary of eleven studies shows a more mixed picture. Four of those studies found that healthy adults experienced less anxiety and an improved sense of wellbeing at daily doses of roughly 0.1 to 3 grams. There was no effect on aggression. Which dose works best and how long you need to take it remain unclear.
For clinical depression, tryptophan does not work well enough on its own. International psychiatric guidelines currently advise against using tryptophan as a standalone treatment, because the study results are too mixed. Other supplements such as omega-3 fatty acids or methylfolate received higher recommendations. If you have a depressive disorder, discuss your options with your doctor.
A small study in older adults (average age 66, thirty participants) showed that a substance the body makes from tryptophan, and then converts into serotonin, improved low mood and thinking ability after eight to twelve weeks at 100 mg per day. However, thirty people is too few to draw firm conclusions.
Combination products containing a small amount of tryptophan (120 mg) led, in one study, to falling asleep three to four minutes faster and to a better mood in the morning. That study was funded by Nestlé, and the product contained several ingredients at once, so what tryptophan itself contributed is unknown. One well-designed study in trained male athletes found no effect whatsoever from a tryptophan combination supplement on sleep or performance, suggesting it may add little for fit, healthy people.
This answer draws on four summaries of multiple studies and three individual studies. The strongest evidence (less time lying awake after falling asleep, at least 1 g per day) comes from a summary combining several studies. For mood, the evidence is more consistent but not unanimous. For depression as a medical condition, the evidence is weak and mixed, and international guidelines state this explicitly. The study on the tryptophan-derived substance and the combination study are too small and too short to allow broad conclusions. The combination study was funded by Nestlé.