The abuse of drugs is a serious universal problem. Drug addiction is considered to be a chronic, relapsing disorder characterized by an uncontrollable drug craving regardless of serious health problems. Repeated drug use arises due to the positive reinforcing effects produced by drugs that lead to neurological changes in the brain’s reward circuits. Drug addiction has also been reported to involve another source of reinforcement such as, withdrawal symptoms. Positive (e.g., euphoria) and negative (e.g., withdrawal symptoms) reinforcement together provide a strong motivational force for obsessive drug intake leading to addiction. The neurological changes and behavioral abnormalities that are associated with drug addiction may persevere for months or years after termination of drug use. The characteristic behaviors of addiction include tolerance, sensitization, dependence, withdrawal and craving.