5-Hydroxytryptophan (5-HTP), used medically as oxitriptan, is a naturally occurring amino acid and chemical precursor as well as a metabolic intermediate in the biosynthesis of the neurotransmitter serotonin.

Brand names include Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum.

Though 5-HTP is found in food only in insignificant quantities, it is a chemical involved intermediately in the metabolism of tryptophan, an amino acid found in all unfractionated foods, with lower total amino acid content correlating with increased tryptophan absorption.

It can be potentiated in combination with a peripherally selective aromatic L-amino acid decarboxylase (AAAD) inhibitor such as carbidopa or benserazide.

5-HTP robustly produces the head-twitch response (HTR) in rodents when administered at relatively high doses.

[15][16] These findings may also explain why selective serotonin reuptake inhibitors (SSRIs) and related serotonergic agents do not produce psychedelic effects.