Potential for cannabis adaptation among participants in a drunk driving intervention

Background: Some alcohol interventions have been found to have the adverse outcome of increasing non-alcohol-related substance use. It is unknown, however, how changes in alcohol use over the course of alcohol ignition interlocks - a common DUI intervention - may impact other substance use. Methods: Alcohol and cannabis use were measured using hair ethylglucuronide and Delta-9-Tetrahydrocannabinol concentrations in blood, respectively. Participants (N = 69) were measured at the interlock installation period and again 6-months later while the interlock was installed. A mixed ANOVA was conducted to examine changes in levels of ethanol and THC over time. Results: On measures of marijuana use, there was a significant interaction effect between the group that increased alcohol use and time F(2, 66) = 7.863, p =.001; partial eta(2) =.192; as well as a main effect for time F(2, 66) = 21.106, p eta(2) =.242. Conclusions: Installing interlocks may inadvertently increase cannabis use among those who decrease alcohol use. Crash risk associated with cannabis use is notably less than that of alcohol use, however, continued cannabis use may be problematic when the device is removed and alcohol use is expected to return to the higher pre-interlock levels.