5-Hydroxytryptophan, more commonly known as 5-HTP, is is derived from the amino acid L-Tryptophan. 5-HTP is converted in the body into the brain chemical messenger serotonin. Serotonin is a neurotransmitter; it helps send messages from one part of the brain to another. Serotonin influences the majority of the cells in the brain, including sleep, appetite, mood.