Added value of mindfulness in a digital cannabis intervention: Three-arm randomized trial

Purpose Digital interventions for cannabis use typically produce small short-term effects that fade over time. This three-arm randomized controlled trial examined whether integrating mindfulness into an established digital cognitive behavioural therapy (CBT) self-help intervention improves the durability of outcomes. Methods We randomized 301 frequent adult cannabis users to Mindfulness CANreduce (mindfulness-enhanced CBT), Standard CANreduce (CBT only), or a waitlist control group with continued access to care as usual. The primary outcome was self-reported cannabis use days in the past 30 days, assessed at 6 weeks, 3 months, and 6 months, and analysed on an intention-to-treat basis using zero-inflated negative binomial mixed models with multiple imputation. Main results Retention was 51.8% at 6 weeks and 31.6% at 6 months, and 6-month attrition did not differ across groups. At 6 weeks, both active interventions reduced cannabis use days relative to the control group (IRR = 0.76, 95% CI [0.64, 0.90]; IRR = 0.80, 95% CI [0.67, 0.95]). At 6 months, the Mindfulness CANreduce group reported fewer use days than both the Standard CANreduce group (IRR = 0.52, 95% CI [0.43, 0.64]) and the control group (IRR = 0.46, 95% CI [0.38, 0.56]), with greater improvements in depressive and anxiety symptoms. Complete-case and tipping-point sensitivity analyses supported these findings, which remain conditional on assumptions about the missing data. Conclusion Integrating mindfulness into a fully automated digital intervention was associated with more durable reductions in cannabis use. Given the low retention and engagement, these findings should be interpreted cautiously.