A new study investigated whether smoking marijuana acutely increased sexual risk on a behavior decision-making task (SRT) and whether sex-related marijuana outcome expectancies influenced sexual risk decisions after marijuana consumption. The study used a 2×2 factorial design to assign participants to one of four groups in which they received a dose of marijuana with 2.8% THC or a placebo and were informed they were given THC or a placebo. Participants (n = 126) were selected from a larger study of the effects of marijuana and impulsivity. Inclusion criteria were age (between 18 and 30 years old) and marijuana use at least weekly in the past month and at least 10 times in the past six months. Exclusion criteria included history of substance use treatment, intent to quit or receive treatment for cannabis misuse, history of certain mental illnesses, and smoking 20 or more cigarettes per day. Participants who reported exclusive homosexual status on the Kinsey scale were also excluded, because the SRT was designed for use with heterosexuals. At baseline, participants’ number of sexual partners, number of new sexual partners, sex-related marijuana expectancies, and intent to engage in sexual risk-reduction behavior (i.e., condom use) were assessed. Total sex-related marijuana expectancy scores were calculated for each participant. The SRT was used to assess participants’ likelihood of having sex without a condom with both a “steady partner” and a “new partner” using filmed, gender-specific scenarios. After smoking marijuana or a placebo and viewing the videos, participants reported their likelihood of using a condom using a six-point scale. The authors used bivariate correlations to examine associations between baseline measures of intent to engage in safe sex, sex-related marijuana expectancies, and post-smoking likelihood of engaging in unprotected sex with a new or steady partner. Multiple regression was used to investigate sex-related marijuana expectancy effects on the likelihood of using a condom on the SRT. For men and women, baseline behavioral intentions were positively correlated with post-smoking ratings of likelihood of unprotected sex, across both types of partners (rs = 0.30 – 0.57, ps < 0.05). For men, sex-related marijuana outcome expectancies were significantly positively correlated with likelihood of having sex without a condom (r = 0.28, p < 0.01). For women, expectancies were positively correlated with this likelihood for a steady partner (r = 0.33, p < 0.05). There was a significant interaction effect observed for marijuana expectancies and drug manipulation observed on the SRT with a new partner (p = 0.02), but, for women, more salient expectancies were associated with increased likelihood of sex without a condom with a steady partner (p = 0.033).
Take away: In this study, the pharmacologic effects of THC did not influence sexual decision making on a sexual risk behavior decision-making task, but sex-related marijuana expectancy outcomes did. These effects were different for men and women.