["Addiction, EarlyView. ", "\nAbstract\n\nAims\nTo 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).\n\n\nDesign\nPhase II, 3‐arm RCT conducted from October 2022 to September 2025, with participants randomized to one of three conditions.\n\n\nSetting\nParticipants 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.\n\n\nParticipants\n149 emerging adults who reported driving under the influence of cannabis at least three times in the past 3 months were enrolled in the RCT.\n\n\nIntervention and comparator\nParticipants 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.\n\n\nMeasurements\nThe 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.\n\n\nFindings\nNegative 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.\n\n\nConclusions\nA 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.\n\n"]