Amphetamine-induced place preference in humans

The conditioned place preference (CPP) procedure is a standard animal model used to study the rewarding properties of drugs. While widely used in preclinical research, it had not been validated in humans. This study aimed to determine if humans would develop a preference for a specific environment paired with d-amphetamine and to investigate whether this preference correlates with the drug's subjective mood-altering effects.

Researchers recruited 31 healthy adults for a five-session study. Participants were divided into a 'paired' group (n=19), who received 20mg of d-amphetamine in one room and a placebo in another, and an 'unpaired' group (n=12), who received both substances in both rooms. During the conditioning sessions, participants completed questionnaires to assess their mood and subjective drug responses. In the final session, participants rated their liking of the two rooms and indicated which room they would prefer for a future session.

The study successfully demonstrated that humans, like non-human animals, exhibit a conditioned place preference. Participants in the paired group rated the amphetamine-associated room significantly higher than the placebo-associated room. Furthermore, the researchers found that an individual's subjective experience of the drug was a strong predictor of this preference: higher ratings of drug-liking and lower ratings of drug-induced anxiety and dysphoria predicted a stronger preference for the drug-paired room.

This research validates the CPP model for human studies, bridging a gap between preclinical and clinical addiction research. By confirming that human place preference is linked to subjective drug responses, the study provides a foundation for future investigations into the neural and psychological mechanisms of drug reinforcement. It also highlights the importance of individual differences in subjective drug responses, suggesting that the reinforcing value of drug-associated environments is not uniform across all users.