Treatment of drug dependence by prescription of a substitute drug for which cross-dependence and cross-tolerance exist. The term is sometimes in reference to a less hazardous form of the same drug used in the treatment. The goals of maintenance therapy are to eliminate or reduce use of a particular substance, especially if it is illegal, or to reduce harm from a particular method of administration, the attendant dangers to health (e.g. from needle sharing) and the social consequences. Maintenance therapy is often accompanied by psychological and other treatment.

Examples of maintenance therapy are the use of methadone for the treatment of heroin dependence and nicotine gum to replace smoking tobacco. Maintenance therapy can last from several weeks to 20 or more years. It is sometimes distinguished from tapering-off therapy (see detoxification).

Maintenance: In the UK context this refers primarily to the pharmacological maintenance of people who are opioid dependent; that is, prescription of opioid substitutes (methadone or buprenorphine). This aims to reduce illicit drug use and its consequent harms (Drug Misuse: Psychosocial Interventions glossary).