Our research at the GCRC during this review period has been focusing on characterizing in humans the effects of drugs of abuse when taken in combination. This experiment examined the effects of acutely-administered d-amphetamine on cigarette smoking. Psychomotor stimulants previously have been found to increase the rate of cigarette smoking, but it has been unclear whether this is due to a specific increase in the reinforcing effects of smoking, or a non-specific increase in the rate of all normally-occurring behaviors. In order to study possible interactions between d-amphetamine and cigarette smoking, we examined the effects of d-amphetamine (0, 7.5, 15 mg/70 kg) on choice between smoking two cigarette puffs and obtaining a monetary reinforcer. Ninety minutes after drug or placebo administration, thirteen male and female subjects had 3 hours in which to make 20 such choices. Each subject received each dose twice, in a mixed order. d-Amphetamine dose-dependently increased smoking choices. CO levels in expired air (a measure of actual smoke inhalation) showed corresponding dose-related increases. In separate sessions, d-amphetamine increased ad lib smoking and CO levels. These results suggest that increases in smoking following d-amphetamine administration are not a result of a non-specific effect on the rate of all normally-occurring behaviors. These results further indicate that d-amphetamine increases the relative reinforcing effects of smoking. We have recently submitted a protocol to continue this general line of research during the next year.
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