Changes in the effects of cocaine during chronic treatment.

The principle object of the study was to identify the changes in the rat's response to cocaine which occurred during chronic administration of the drug. Doses of 20 and 35 mg/Kg cocaine were administered at intervals of 12 and 24 hours, for 300 days or until their effects proved fatal. Four main effects were observed: sensitization to cocaine's convulsant and behavioral activating properties, tolerance to its weight loss effects and decreased response duration. Convulsant sensitization occurred primarily among rats receiving the higher dose of cocaine. All other effects occurred with equal frequency in rats at both doses. None of the changes were dependent on the interval between injections.