Behavior seeking. A person is addicted to a substance when their behavior changes to the point where they do not care about the consequences of their choices, even if it involves the legal system, and will do whatever is needed to get the substance.
Brain Chem change. Addiction can also be viewed as a continued involvement with a substance or activity despite the negative consequences associated with it. Pleasure, enjoyment or relief from actual or perceived ailments would have originally been sought; however, over a period of time involvement with the substance or activity is needed to feel normal.