A Psychomotor Stimulant Theory of Addiction

The theory is advanced that the common denominator of a wide range of addictive substances is their ability to cause psychomotor activation. This view is related to the theory that all positive reinforcers activate a common biological mechanism associated with approach behaviors and that this mechanism has as one of its components dopaminergic fibers that project up the medial forebrain bundle from the midbrain to limbic and cortical regions. Evidence is reviewed that links both the reinforcing and locomotor-stimulating effects of both the psychomotor stimulants and the opiates to this brain mechanism. It is suggested that nicotine, caffeine, barbiturates, alcohol, benzodiazepines, cannabis, and phencyclidine-each of which also has psychomotor stimulant actions-may activate the dopaminergic fibers or their output circuitry. The role of physical dependence in addiction is suggested to vary from drug to drug and to be of secondary importance in the understanding of compulsive drug self-administration.