Cannabis use during treatment for alcohol use disorders predicts alcohol treatment outcomes.

AIMS: To compare post-treatment alcohol use between those who use cannabis and those who abstain during treatment for alcohol use disorders (AUD); and to examine potential cannabis use thresholds by comparing post-treatment alcohol use between four frequency groups of cannabis users relative to abstainers.

DESIGN: Secondary analyses of the Combined Pharmacotherapies and Behavioral Interventions (COMBINE) Study, a randomized control trial of AUD treatments. The current study compares longitudinal drinking data between those who used cannabis versus those who abstained during COMBINE treatment.

SETTING: The COMBINE Study treatments were delivered on an out-patient basis for 16 weeks. The current analyses include 206 cannabis users and 999 cannabis abstainers.

PARTICIPANTS: All participants met diagnosis of primary alcohol dependence (n = 1383).

MEASUREMENTS: Primary exposures were any cannabis use and quartiles of cannabis use (Q1: 1-4 use days during treatment, Q2: 5-9 days, Q3: 10-44 days, Q4: 45-112 days). Outcomes were percentage of days abstinent from alcohol (PDA), drinks per drinking day (DPDD) and percentage of heavy drinking days (PHD), all measured at treatment end and 1 year post-treatment.

FINDINGS: Compared with no cannabis use, any cannabis use during treatment was associated with 4.35% [95% confidence interval (CI) = -8.68, -0.02], or approximately 4 fewer alcohol abstinent days at the end of treatment. This association weakened by 1 year post-treatment (95% CI = -9.78, 0.54). Compared with no cannabis use, only those in the second quartile of cannabis use (those who used once or twice per month during treatment) had 8.81% (95% CI = -17.00, -0.63), or approximately 10 fewer days alcohol abstinent at end of treatment, and 11.82% (95% CI = -21.56, -2.07), or approximately 13 fewer alcohol abstinent days 1 year post-treatment. Neither any cannabis use nor quartiles were associated with DPDD or PHD at either time-point.

CONCLUSIONS: Among individuals in alcohol treatment, any cannabis use (compared with none) is related to a significantly lower percentage of days abstinent from alcohol post-treatment, although only among those who used cannabis once or twice per month.