Clonidine is a central alpha adrenergic agonist which can be used to treat the opiate withdrawal syndrome. It has been used in many controlled trials and a substantial body of research evidence is available about its effectiveness in this role. This paper reviews the literature regarding its introduction in the Yale studies, its effectiveness relative to gradual methadone reduction treatments, its side effects, and touches briefly upon its use in conjunction with opiate antagonists. It is concluded that clonidine produces marked reduction of withdrawal symptoms but does not eliminate them; that the pattern of withdrawal symptoms differs from that associated with methadone reduction schemes; that there is some disagreement about the clinical significance of hypotensive and other side effects; and that the drug has interesting possibilities for rapid withdrawal programmes when combined with naltrexone.