5-HTP, also known as 5-hydroxytryptophan, is the direct precursor to the neurotransmitter serotonin. Low levels of serotonin are considered to be a break down in support for a range of things. Many people that are afflicted with one of those conditions often have others, which has led some researchers to label them collectively as "Low Serotonin Syndrome".
Serotonin is an important initiator of sleep. In numerous studies, 5-HTP has been shown to decrease the time required to get to sleep, increases REM sleep and deep sleep.
By increasing the brain’s concentration of serotonin, an antidepressant effect is created. 5-HTP works by increasing the amount of serotonin manufactured in the brain. Although systematically administered serotonin does not readily enter the brain, its direct precursor, 5-HTP does penetrate the blood-brain barrier, and therefore, dietary consumption of 5-HTP leads to an increase in brain serotonin concentration.