An addiction is defined as a chronic neurobiological disorder that has genetic, psychosocial and environmental factors. Addiction has both physical and psychological componants.
Physical dependence occurs when tolerance to a drug has developed and negative physical symptoms occur with abrupt discontinuation or reduced dose of the drug (withdrawal). Common drugs that are known to cause physical dependence include alcohol, amphetamines, benzodiazepines, caffeine, cocaine and opiates (such as heroin) among others. Dopamine is believed to play an important role in the development of physical dependence and all of the drugs mentioned previously have some affect on dopamine in the brain.