L-tryptophan from the capsules enters the bloodstream and reaches the brain, where it is converted first into 5-hydroxytryptophan (5-HTP) and then into serotonin. Serotonin is a neurotransmitter often called the "well-being molecule"; it participates in mood regulation, appetite control, and stress tolerance. In the evening, part of the serotonin is converted into melatonin, which helps the body prepare for sleep and adjust to the natural day–night rhythm.
This explains why many people take tryptophan in the evening: its conversion into melatonin is most active then. It is not a sleeping pill. Instead, the body uses the amino acid at its own pace, and the outcome depends on the whole daily routine, light exposure, and usual sleep habits. Some people prefer this approach over taking melatonin directly, because tryptophan gives the body a building block and the body itself regulates how much serotonin and melatonin it produces from it.
Because serotonin is involved in mood and emotional balance, the supplement may be of interest to people going through a tense period or to those who feel mood swings during dark winter months. This does not replace medical care. If sleep problems, low mood, or anxiety are persistent, a doctor should be consulted. The product is not intended to diagnose, treat, or prevent any disease.