Serotonin (5-Hydroxytryptamine) (Standard) hydrochloride is the analytical standard of Serotonin hydrochloride (HY-B1473). This product is intended for research and analytical applications. Serotonin (5-Hydroxytryptamine) hydrochloride is a monoamine neurotransmitter in the CNS and an endogenous 5-HT receptor agonist. Serotonin hydrochloride is also a catechol O-methyltransferase (COMT) inhibitor with a Ki of 44 µM.