ADDICTION is a primary, chronic, neurobiologic disease, with genetic, psychosocial, and environmental factors influencing its development and manifestations. It is characterized by behaviors that include one or more of the following: impaired control over drug use, compulsive use, continued use despite harm, and craving.

PHYSICAL DEPENDENCE is a state of adaptation that is manifested by a drug class specific withdrawal syndrome that can be produced by abrupt cessation , rapid dose reduction, decreasing blood level of the drug, and/or administration of an antagonist.

TOLERANCE is a state of adaptation in which exposure to a drug induces changes that result in a diminution of one or more of the drug's effects over time.

PSEUDOADDICTION is a term which has been used to describe patient behaviors that may occur when pain is undertreated. Patients with unrelieved pain may become focused on obtaining medications, may clock watch, and may otherwise seem inappropriately "drug seeking". Even such behaviors as illicit drug use and deception can occur in the patient's efforts to obtain relief. Pseudoaddiction can be distinguished from true addiction in that the behaviors resolve when pain is effectively treated.

The above definitions are directly from the American Pain Society. These definitions are endorsed by the American Academy of Pain Medicine, the American Pain Society and the American Society of Addiction Medicine.