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

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.

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.

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.

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

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.

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.

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.