Strictly speaking, an addiction is a compelling physical and psychological need for a habit forming chemical substance, without regard for destructive consequences. In recent years, this definition has been expanded to include practically any kind of compulsive behaviour ranging from over exercise to compulsive gambling to shoplifting and sex. There are now more than 200 such addictions that are being addressed by 12-step groups modeled on Alcoholics Anonymous.

The chemical addictions most prevalent are nicotine, alcohol, crack cocaine, heroin, amphetamines and other prescription drugs. No one fully understands why the use of these substances evolves into abuse or addiction in some individuals and not in others.

However, research points out to at least three possible explanations; a genetic predisposition, an abnormality in brain chemistry and a personality disorder. Most likely it is a combination of these factors that leads to addiction.