Phentermine self-administration in naive free-feeding and food-deprived rats: a dose response study.

In the present experiment graded doses of phentermine, an anorectic similar to amphetamine in structure and mechanism of action, were made available to naive free-feeding (FF) or 80% free-feeding weight (FFW) rats for IV self-administration. Findings showed that, in 80% FFW rats, the number of injections taken were an inverted U-shaped function of dose, whereas the amount of drug injected was a monotonically increasing function of dose. FF animals, however, failed to self-administer phentermine at rates that differed significantly from FF animals self-administering saline. These data suggest that the clinical use of anorectics which have a mechanism of action similar to amphetamine may increase the risk of drug dependence whenever weight loss is achieved.