reserpine (rĕsûrˈpēn) [key], alkaloid isolated from the root of the snakeroot plant ( Rauwolfia serpentina ), a small evergreen climbing shrub of the dogbane family native to the Indian subcontinent. Known in India as Sarpaganda, it was used for centuries to treat insanity as well as physical illnesses such as fevers and snakebites. After its isolation in 1952 it was used to lower high blood pressure, but its property of producing severe depression as a side effect also made it useful in psychiatry as a tranquilizer in the control of agitated psychotic patients. It has largely been replaced in psychiatric use by the phenothiazine tranquilizers, although it is still used as an experimental tool in the study of psychosis. Reserpine causes many toxic side effects including nightmares, Parkinsonism (see Parkinson's disease), and gastrointestinal disturbances.