Wiki on Addiction:
Addiction exacts a high toll on individuals and society as a whole through the direct adverse effects of drugs and associated healthcare costs, the functional consequences of altered neuroplasticity in the brain, and the loss of productivity. Classic hallmarks of addiction include impaired control over substances or behavior, preoccupation with substance or behavior, continued use despite consequences, and denial. Habits and patterns associated with addiction are typically characterized by immediate gratification (short-term reward), coupled with delayed deleterious effects (long-term costs).
Also possibly useful from wiki: