1,2,3,4-Tetrahydro-β-carboline is a serotonin reuptake inhibitor (IC = 7.4 µM in rat brain homogenates) and metabolite of tryptamine . In vivo, 1,2,3,4-tetrahydro-β-carboline (20 and 40 µg/animal, i.c.v.) reduces serotonin levels in rat forebrain. It induces serotonin-mediated hyperactivity syndrome (HHS) in rats (ED = 48 mg/kg). 1,2,3,4-Tetrahydro-β-carboline (6.25-75 mg/kg) also reduces acetic acid-induced writhing in rats.