5-HTP (5-Hydroxytryptophan) is an amino acid. It can be taken as a supplement in tablet/capsule form.
5-HTP works in the brain and central nervous system by increasing the production of the chemical serotonin. Serotonin can affect mood, sleep, appetite, temperature, sexual behavior, and pain sensation. Since 5-HTP increases the synthesis of serotonin, it is used for several diseases where serotonin is believed to play an important role, including depression, insomnia, obesity, and many other conditions.
Although there are some placebo-controlled studies indicating a benefit of 5-HTP, it is not yet accumulated enough evidence to be approved by the FDA for the treatment of any disorder. More research is needed.