The effect of an interactive mobile phone‐based brief intervention on driving under the influence of cannabis among emerging adults: A randomized controlled trial

AIMS: To examine the efficacy of a mobile phone-based brief intervention aimed at reducing driving under the influence of cannabis among emerging adult cannabis users in the context of a randomized 3-group randomized clinical trial (RCT). DESIGN: Phase II, 3-arm RCT conducted from October 2022 to September 2025, with participants randomized to one of three conditions. SETTING: Participants were recruited from Western Kentucky University in Bowling Green, KY, and the surrounding community within a 60-mile radius. All interventions were delivered remotely via mobile phone. PARTICIPANTS: 149 emerging adults who reported driving under the influence of cannabis at least three times in the past 3 months were enrolled in the RCT. INTERVENTION AND COMPARATOR: Participants in the personalized feedback and motivational interviewing text messaging group (PF + MIT; n = 45) received personalized feedback on substance-impaired driving plus a series of interactive, motivational interviewing-style text messages delivered by a trained graduate student over a single session. Participants in the personalized feedback group (PF; n = 50) received personalized feedback only. The information control group (IC; n = 54) received standard, non-personalized substance use information. MEASUREMENTS: The primary outcome was the number of times driving under the influence of cannabis in the past 3 months, which was self-reported via mobile web survey during follow-up assessments at 3 and 6 months post-intervention. The secondary outcome was the number of times driving after simultaneous alcohol and cannabis use in the past 3 months. FINDINGS: Negative binomial mixed models analyses indicated that participants in the PF + MIT group showed statistically significantly greater reductions in driving under the influence of cannabis at 3 months compared with the IC group [incidence rate ratio (IRR) = 0.34, 66% reduction; P < 0.001] and maintained reductions at 6 months (IRR = 0.40, 60% reduction; P < 0.001). Participants in the PF group demonstrated statistically significant reductions in driving under the influence of cannabis at 6 months relative to the IC group (IRR = 0.25, 75% reduction; P < 0.001). No statistically significant differences over time between groups were found for the number of times driving after simultaneous use of alcohol and cannabis. CONCLUSIONS: A randomized clinical trial found that personalized feedback and motivational interviewing text messaging accelerated reductions in driving under the influence of cannabis at 3-month follow-up compared with controls, and personalized feedback alone showed delayed reductions in driving under the influence of cannabis at 6-month follow-up compared with controls.