Can cannabis use be prevented by targeting personality risk in schools? Twenty‐four‐month outcome of the adventure trial on cannabis use: a cluster‐randomized controlled trial

AIMS: To examine the effectiveness of a personality‐targeted intervention program (Adventure trial) delivered by trained teachers to high‐risk (HR) high‐school students on reducing marijuana use and frequency of use. DESIGN: A cluster‐randomized controlled trial. SETTING: Secondary schools in London, UK. PARTICIPANTS: Twenty‐one secondary schools were randomized to intervention (n = 12) or control (n = 9) conditions, encompassing a total of 1038 HR students in the ninth grade [mean (standard deviation) age = 13.7 (0.33) years]. INTERVENTIONS: Brief personality‐targeted interventions to students with one of four HR profiles: anxiety sensitivity, hopelessness, impulsivity and sensation‐seeking. MEASUREMENTS: Primary outcome: marijuana use. Secondary outcome: frequency of use. Assessed using the Reckless Behaviour Questionnaire at intervals of 6 months for 2 years. Personality risk was measured with the Substance Use Risk Profile Scale. FINDINGS: Logistic regression analysis revealed significant intervention effects on cannabis use rates at the 6‐month follow‐up in the intent‐to‐treat sample [odds ratio (OR) = 0.67, P = 0.05, 95% confidence interval (CI) = 0.45–1.0] and significant reductions in frequency of use at 12‐ and 18‐month follow‐up (β = –0.14, P ≤ 0.05, 95% CI = –0.6 to –0.01; β = –0.12, P ≤ 0.05, 95% CI = –0.54 to 0.0), but this was not supported in two‐part latent growth models. Subgroup analyses (both logistic and two‐part models) reveal that the sensation‐seeking intervention delayed the onset of cannabis use among sensation seekers (OR = 0.25, β = –0.833, standard error = 0.342, P = 0.015). CONCLUSIONS: Personality‐targeted interventions can be delivered effectively by trained school staff to delay marijuana use onset among a subset of high‐risk teenagers: sensation‐seekers.