Psychotherapeutic drugs have dramatically improved the prognosis for patients with severe mental illness. The drug treatments are not a panacea. The medications sometimes cause irreversible side effects, and they are not helpful for all patients. They allow large numbers of individuals to leave the hospital, but to return to communities that are often poorly prepared to provide continuing care. Despite their limitations, psychotherapeutic drugs relieve a great deal of human suffering. They also involve psychiatry in modern biological science. This has led to the continuing search for more effective medications based on the study of possible biochemical substrates of psychiatric disorders.