COCAINE ABUSE AND DEPENDENCE

Western countries experienced a widespread cocaine epidemic during the 1980s, and the number of frequent users has not declined in this decade. A key factor in the development of this epidemic has been the introduction of ''crack,'' an affordable form of cocaine that appears to be more addicting than the powder. Epidemiologic studies indicate a high incidence of polysubstance abuse among cocaine abusers and probable gender differences in patterns of abuse and response to treatment. An abstinence syndrome has been documented in outpatients after the acute cessation of cocaine; the symptoms perhaps depend on the presence of cues to evoke craving of cocaine and thus are not detected in inpatient settings. Cocaine is a psychostimulant drug that possesses euphorigenic and reinforcing properties. The fact that various animal species self-administer cocaine through the intravenous route provides a reliable animal model for the study of the molecular mechanism of cocaine action and for the characterization of the anatomical substrates responsible for the rewarding properties of the drug. A multisynaptic, allocorticolimbic-accumbens-pallidal circuitry has been identified that seems to play an important role. This pathway may also be part of the neuronal substrates that mediate the reinforcing properties of other classes of abused drugs and, perhaps, motivated behavior in general. Because of this potent reinforcing nature of cocaine in humans, the problem of designing effective therapy for its addiction has not been simply solved. Clinical treatments, guided by animal studies and designed for specific attack of symptoms of the abstinence syndrome, craving and anhedonia, have been tested. To date, only a few agents have proved effective in controlled trials (amantadine, bromocriptine, carbamazepine, and desipramine) and these have limitations of side effects or delayed onset of action. Agents that interact with specific subcomponents of the dopamine system or its connections offer promise for the development of successful agents to treat cocaine abuse and craving in humans.