Substance Dependence, commonly called drug addiction, is a compulsive need to use drugs in order to function normally. When such substances are unobtainable, the user suffers from withdrawal.
According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), substance dependence is defined as:
When an individual persists in use of alcohol or other drugs despite problems related to use of the substance, substance dependence may be diagnosed. Compulsive and repetitive use may result in tolerance to the effect of the drug and withdrawal symptoms when use is reduced or stopped. This, along with Substance Abuse are considered Substance Use Disorders….
Substance Dependence can be diagnosed with physiological dependence, evidence of tolerance or withdrawal, or without physiological dependence. The DSM-IV does not use the word addiction at all.