Drug rehabilitation is a term for the processes of medical or psychotherapeutic treatment, for dependency on psychoactive substances

Psychoactive drug

A psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...

 such as alcohol

Alcoholic beverage

An alcoholic beverage is a drink containing ethanol, commonly known as alcohol. Alcoholic beverages are divided into three general classes: beers, wines, and spirits. They are legally consumed in most countries, and over 100 countries have laws regulating their production, sale, and consumption...

, prescription drugs

Medical prescription

A prescription is a health-care program implemented by a physician or other medical practitioner in the form of instructions that govern the plan of care for an individual patient. Prescriptions may include orders to be performed by a patient, caretaker, nurse, pharmacist or other therapist....

, and so-called street drugs such as cocaine

Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...

, heroin or amphetamines. The general intent is to enable the patient to cease substance abuse, in order to avoid the psychological, legal, financial, social, and physical consequences that can be caused, especially by extreme abuse.
Psychological dependency is addressed in many drug rehabilitation programs by attempting to teach the patient new methods of interacting in a drug-free environment.