5-Hydroxytryptophan (5-HTP) is an amino acid that is converted in the body to produce serotonin, the neurotransmitter responsible for healthy mood and proper sleep. Low serotonin levels have been reported to be associated with depression, anxiety, sleep disorders, weight gain, and other health problems. Increasing your body’s production of serotonin may have various benefits. 5-HTP may be used during the day to support healthy mood or appetite or at bedtime to support sleep.