RESEARCH ARTICLE A Preliminary Investigation of Individual Differences in Subjective Responses to D- Amphetamine, Alcohol, and Delta-9- Tetrahydrocannabinol Using a Within- Subjects Randomized Trial

Polydrug use is common, and might occur because certain individuals experience positive effects from several different drugs during early stages of use. This study examined individ-ual differences in subjective responses to single oral doses of d-amphetamine, alcohol, and delta-9-tetrahydrocannabinol (THC) in healthy social drinkers. Each of these drugs pro-duces feelings of well-being in at least some individuals, and we hypothesized that subjec-tive responses to these drugs would be positively correlated. We also examined participants ’ drug responses in relation to personality traits associated with drug use. In this initial, exploratory study, 24 healthy, light drug users (12 male, 12 female), aged 21–31 years, participated in a fully within-subject, randomized, counterbalanced design with six 5.5-hour sessions in which they received d-amphetamine (20mg), alcohol (0.8 g/kg), or THC (7.5 mg), each paired with a placebo session. Participants rated the drugs ’ effects on both global measures (e.g. feeling a drug effect at all) and drug-specific measures. In gen-eral, participants ’ responses to the three drugs were unrelated. Unexpectedly, “wanting more ” alcohol was inversely correlated with “wanting more ” THC. Additionally, in women