As a general term, the state of needing or depending on something or someone for support or to function or survive. As applied to opioids, implies the need for repeated doses of a drug to feel good or to avoid feeling bad.

In 1964, a World Health Organization (WHO) Expert Committee introduced the term “dependence” to replace addiction and habituation. The term can generally be used with reference to dependence on any psychoactive drugs (e.g. drug dependence, chemical dependence, substance dependence), or with specific reference to a particular drug or class of drugs (e.g. opioid dependence). Although ICD-10 has a specific definition for dependence, described in terms applicable across drug classes, the symptoms of dependence will vary for each specific drug.

Dependence often refers to both the physical and psychological elements of drug dependence. More specifically, psychological or psychic dependence refers to the experience of impaired control over drug use (including cravings and compulsions to use drugs) while physiological or physical dependence refers to tolerance and withdrawal symptoms (see neuroadaptation). However, in biologically oriented discussion, dependence is often used to refer only to physical dependence.

Dependence or physical dependence is also used in a narrower sense in the psychopharmacological context, to refer solely to the development of withdrawal symptoms on cessation of drug use.