The use and misuse of drugs have been documented for millennia. While the initial choice to use drugs is usually voluntary, adaptive changes in the brain occur over time such that the individual becomes obsessed with seeking out and consuming drugs despite awareness of the risks associated with doing so. This is called addiction.

As clinicians, we define addiction as a chronic relapsing brain disease characterized by compulsive drug-seeking behavior and consumption of drug(s) with loss of control in limiting consumption. Over time, tolerance and drug dependence develop.

Tolerance may be defined as a decline in the effects of a drug with continued use at the same dose; therefore, increasing doses of the drug are needed over time to elicit the same response.

Dependence means withdrawal symptoms occur when the drug is stopped or access to the drug is cut off.