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Addiction is differentiated from psychological dependence and physical dependence.
Psychological dependence is the feeling that someone has when they think that drugs or activities are necessary to achieve a feeling of well-being. Physical dependence is marked by the development of tolerance to a drug or activity's effects so that increased amounts of a drug or activity are needed to obtain the desired effect. Tolerance also reveals its presence by the development of withdrawal symptoms when the drug or activity is stopped for a sufficient time. These matters are more complex than often thought. Norman E. Zinberg, who passed away in 1989, was an innovator in the field of psychiatry and addictive behaviors.