5HTP (5-Hydroxytryptophan)

5-Hydroxytryptophan (5-HTP), also known as oxitriptan (INN), is a naturally occurring amino acid and chemical precursor as well as metabolic intermediate in the biosynthesis of the neurotransmitters serotonin and melatonin from tryptophan. 5-Hydroxytryptophan is decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) by the enzyme aromatic-L-amino-acid decarboxylase with the help of vitamin B6.[4] This reaction occurs both in nervous tissue and in the liver.5-HTP crosses the blood-brain barrier,[6] while 5-HT does not.

Since 5-HTP incresease levels of serotonin, it is used to treat depression, sleep disorders and pain.