Opioid Agonist Treatment, or OAT, refers to the treatment of a narcotics addiction in humans via the administration of similar opioid drugs, agonists, and the resultant cross tolerance and physical dependence. Methadone and Buprenorphine are the most common drugs used in agonist treatment. Methadone is a full opioid agonist and so is the preferred treatment in heroin addiction as it creates a feeling of euphoria, though not as strong as from taking heroin; however, after repeated doses, tolerance develops to the euphoric effects of methadone and eventually becomes minimal or nonexistent. Buprenorphine is a partial opioid agonist and has substantially less severe withdrawal effects versus methadone and other strong opioids making it very desirable as a treatment. However, the high from Buprenorphine is also reduced leading to addicted individuals preferring methadone treatment.
The use of agonist drugs to treat a narcotics addiction is tightly regulated in the United States. Diversion, or potential diversion, of agonist drugs is often the domain of the Drug Enforcement Administration, as they are defined as criminal acts. Only facilities accredited by CSAT, the Center for Substance Abuse and Treatment, part of the Department of Health and Human Services, are able to provide this service in the U.S.