Addiction is a chronic disorder proposed to be precipitated by a combination of genetic, biological/pharmacological and social factors. Addiction is characterized by the repeated use of substances or behaviors despite clear evidence of morbidity secondary to such use.

There is a lack of consensus as to what may properly be termed 'addiction.' Some within the medical community maintain a rigid definition of addiction and contend that the term is only applicable to a process of escalating drug or alcohol use as a result of repeated exposure. However, addiction is often applied to compulsive behaviors other than drug use, such as overeating or gambling. These behavioral addictions, however, almost never exist without another addiction to some substance . In all cases, the term addiction describes a chronic pattern of behavior that continues and is perceived to be hard or impossible to quit at any time. It is quite common for an addict to express the desire to stop the behavior, but find himself or herself unable to cease.

Addiction is often characterized by an ongoing effort to use more (drug or behavior), tolerance, and withdrawal symptoms in the absence of the stimulus. Many drugs and behaviors that provide either pleasure or relief from pain pose a risk of addiction or dependency.