(5-hydroxytryptamine; 5-hydroxy-3-(β-aminoethyl)indole). CAS 50-67-9. C10H12N2O. A powerful vasoconstrictor occurring in the brain and blood platelets, it is thought to play a part in regulation of blood pressure and also has muscle-contracting properties. It has been isolated from beef serum and may be synthesized from 5-benzyloxyindole. Serotonin is similar to the hallucinogenic drugs mescaline, LSD, psilocin, and psilocybin. Its formation is inhibited by p-chlorophenylalanine.