Caffeine choice prospectively predicts positive subjective effects of caffeine and d-amphetamine

Background: Individuals vary in their subjective and behavioral response to psychomotor stimulants and these differences may be associated with the likelihood of developing problematic use of these drugs. The present study sought to determine whether individual differences in caffeine choice prospectively predict subjective response to acute doses of caffeine and d-amphetamine. Methods: In Phase 1, Choosers and Nonchoosers of caffeine were identified using 10 independent choice trials in which subjects repeatedly chose between caffeine (200. mg/70. kg) and placebo. Choosers were defined as those who chose caffeine over placebo on ≥7 of the 10 trials; Nonchoosers were those who chose placebo on ≥7 trials. In Phase 2, Choosers and Nonchoosers were compared in their subjective response to caffeine (100, 200, 400. mg/70. kg) and d-amphetamine (5, 10, 20. mg/70. kg). Results: Of the 22 participants completing the study, 11 met criteria for being a caffeine Chooser and 8 were Nonchoosers. In Phase 1, Choosers reported higher ratings of positive (i.e., pleasant) and lower ratings of negative (i.e., unpleasant) effects of caffeine during the sampling sessions. In Phase 2, caffeine Choosers reported more positive subjective effects and fewer negative effects of caffeine and d-amphetamine, particularly at the highest doses examined. Conclusions: Individual differences in caffeine reinforcement predicted subsequent subjective response to both d-amphetamine and caffeine. This observation may have clinical utility for identifying individuals who are vulnerable to the reinforcing effects of abused psychomotor stimulants.