Academic detailing’s effectiveness was first documented in a randomized controlled trial of 435 physicians seeing patients in four Medicaid programs. Based on Medicaid claims tapes from the four states, moderate to high prescribers of drugs were identified and randomly assigned to receive academic detailing visits, mailings, or control (no intervention). Physicians who were offered academic detailing visits significantly reduced their prescribing of target drugs by 14% compared with controls. The effect persisted for at least nine months, post-intervention. In addition, no significant increase in the use of costly substitute drugs was identified