Group therapy for women with substance use disorders: In-session affiliation predicts women's substance use treatment outcomes.

In-session affiliation among members is a hypothesized mechanism of action of group therapy for women with substance use disorders (SUDs). We evaluated group affiliation as an independent predictor of SUD treatment outcome in women (n = 100), 18 years or older diagnosed with substance dependence, who were randomized to the single-gender Women's Recovery Group (WRG) or mixed-gender group therapy (Group Drug Counseling; GDC). Affiliative statements made by members in both groups were measured for 39 women in each treatment arm. We studied the relationship between frequency of affiliative statements categorized in quintiles and the trajectory of days of any drug use during 3 months treatment and 6 months post-treatment using a Poisson regression model with estimation via generalized estimating equations. Furthermore, we investigated whether the effect of affiliation on substance use was moderated by group therapy type. The relationship between amount of affiliation and substance use reduction was non-linear. At the end of the treatment phase (3 months), women who experienced the highest level of affiliation (>65 affiliative statements on average) were found to reduce substance use by about 1.75 days more (p-value = 0.02) than women who experienced the lowest level of affiliation (<26). The effects of affiliation persisted 6 months post-treatment and were moderated by therapy group, whereby women enrolled in the single-gender WRG appeared to benefit more from affiliation post-treatment. Training therapists to facilitate verbal affiliation may provide added therapeutic benefit to group therapy for women with SUDs.