Efficacy of a Web-Based Tailored Intervention to Reduce Cannabis Use Among Young People Attending Adult Education Centers in Quebec

BACKGROUND: Cannabis use is common among young adults. Web-based interventions are an increasingly popular way to reach this population. The aim of this study was to evaluate the efficacy of a Web-based tailored intervention, developed on theoretical and empirical grounds, to reduce cannabis use among young people by promoting a more positive intention to abstain. METHODS: An experimental design was employed to evaluate the efficacy of the intervention in reducing cannabis use (primary outcome) by bolstering intention (secondary outcome) to abstain from use. Participants were randomly assigned either to an experimental group that received the Web-based tailored intervention or to a control group that did not. RESULTS: Of 588 young adults (18-24 years of age) recruited, 295 were randomly assigned to the experimental group and 293 to the control group. At baseline, 343 reported using cannabis at least once in the past year. An intention-to-treat analysis showed that, at postintervention, a higher proportion of participants in the experimental group had reduced their cannabis use compared with the control group [10.8% vs. 5.1%, χ2(2) = 9.89, p = 0.007]. A mixed model for repeated measures revealed a statistically significant difference in terms of change in intention to abstain from cannabis use in the coming month [Group × Time interaction, F(1,474) = 8.03, p = 0.005]: intention increased for the experimental group (5.07 ± 2.07 to 5.45 ± 1.88; p