Increased drinking in a trial of treatments for marijuana dependence: substance substitution?

This report examines whether participants in a study of treatments for marijuana dependence may have increased their use of alcohol when they reduced or ceased marijuana use. Participants were randomly assigned to one of four psychosocial treatments and followed at 3-month intervals for 1 year. Findings are from 207 cases with data at posttreatment and at least one other follow-up. 73% of cases reported an increase of at least 10% in drinking days over their level at intake, and 65% reported an increase of at least 10% in drinks per drinking day. Drinking increases were not related to treatment condition nor to change in marijuana use, but were related to baseline drinking: those with less baseline drinking tended to increase their drinking during treatment and those with more baseline drinking reported less drinking during treatment. Thereafter, drinking levels remained fairly stable throughout the follow-up year. The results are most likely reflective of a regression to the mean effect, and indicate that use of alcohol and marijuana are independent of one another.