Addiction is defined as a state in which the body relies on a substance or activity for normal functioning and develops a physical dependence on that substance or a psychological dependence on that activity. It is generally accepted that addiction is a state of disease, however not all doctors agree on the exact nature of the addiction or dependency. Certain mood disorders and anxiety orders can also overlap into addiction.
When the substance or activity that the individual is dependent upon is removed or stopped it causes a withdrawal, resulting in both physical and/or psychological symptoms. The individual uses an addictive substance or activity as a way to induce pleasure initially, but with continued use the goal becomes relieving the anxiety caused by the absence of a given addictive substance. This sets up the cycle of compulsive behavior.