Aims
(1) Compare post-treatment alcohol use between those who use cannabis and those who abstain during treatment for alcohol use disorders (AUD). (2) 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 COMBINE Study, a randomized control trial of AUD treatments. The current study compares longitudinal drinking data between those who used cannabis vs. those who abstained during COMBINE treatment.
Setting
The COMBINE Study treatments were delivered on an outpatient basis over 16 weeks. The current analyses include 206 cannabis users and 999 cannabis abstainers.
Participants
All participants met diagnosis of primary alcohol dependence (N = 1,383).
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 percent days abstinent from alcohol (PDA), drinks per drinking day (DPDD), and percent heavy drinking days (PHD), all measured at treatment end and one year post-treatment.
Findings
Compared with no cannabis use, any cannabis use during treatment was associated with 4.35% (95% CI: −8.68, −0.02), or approximately four fewer alcohol abstinent days at the end of treatment. This association weakened by one-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 ten fewer days alcohol abstinent at end of treatment, and 11.82% (95% CI: −21.56, −2.07), or approximately 13 fewer alcohol abstinent days one-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 significantly lower percent days abstinent from alcohol post-treatment, though only among those who used cannabis once or twice per month.