Nearly 90% of the studies investigating gender differences in substance abuse treatment outcomes were published since 1990, and of those, about 40% were published since the year 2000. Only about 12% of these studies were randomized clinical trials. Much of the available information is derived from cross-sectional, descriptive, quasi-experimental, and observational studies. We are in the very earliest stage of establishing our base of valid and reliable information. Certain findings have been replicated in a number of studies across different populations, however, and areas where results are conflicting point the way to where future research may be most illuminating.
A convergence of evidence suggests that women with substance use disorders are less likely than their male counterparts to enter treatment over their lifetime. Complex socio-cultural and socioeconomic factors are associated with women's entry into substance abuse treatment. In the past, perceived social stigma may have hindered women's help-seeking patterns for substance abuse treatment and contributed to their under-diagnosis, under-detection, and lower rates of referral to treatment. Changes in the treatment system and social attitudes related to alcohol and drug use, as well as increased acceptability of treatment seeking, over the past 20 years may have influenced help-seeking patterns among women, but little is currently known about these changes. There is evidence that economic disparities, lower educational attainment, and fewer social supports among women compared to men influence access to substance abuse treatment and treatment entry. Addressing heightened need among women for vital ancillary services such as childcare, perinatal treatment, and family services could enhance access to substance abuse treatment for many women.
Evidence demonstrates that gender is not necessarily a significant predictor of retention, completion, or outcome once an individual begins treatment. Retention and longer length of treatment have been positively associated with substance abuse treatment outcomes for both women and men. Certain characteristics that are associated with treatment retention appear to vary by gender. For example, greater levels of psychological functioning and lower levels of psychiatric symptoms; socioeconomic status, such as higher income, employment, and educational attainment; social support; and personal and social stability are all associated with treatment retention. Many of these predictors vary by gender and have been found to be associated with women's retention in substance abuse treatment. Importantly, certain lines of evidence indicate that specific programming designed to address some of these circumstances, such as the negative effects of social instability, can enhance satisfaction with treatment and increase retention.
With respect to the outcomes of substance abuse treatment, an older literature reflected a belief that women would have worse substance abuse treatment outcomes than men. The literature reviewed here does not substantiate this. In fact, there are a number of studies that demonstrate better treatment outcomes for women than men with substance use disorders. This review would suggest that examining gender as a dichotomous independent predictor of treatment outcome is no longer the most effective line of investigation for substance abuse treatment research. Conversely, the interaction between certain baseline characteristics and gender has not been ascertained in many instances. For example, there are few treatment outcome studies that have had adequate sample sizes to test gender as it interacts with race, ethnicity, or age (e.g., adolescence, young adult, older adult).
The results of this review suggest that there are a number of target characteristics that are associated with treatment outcomes that often vary by gender. For example, treatment outcome may be affected by socioeconomic characteristics (e.g., educational attainment, employment, dependent children), co-occurring psychiatric disorders, history of victimization (e.g., sexual and physical assault in childhood and/or adulthood), type of services used and number of hours in treatment, relapse patterns, and therapist-patient gender matching. Each of these patient- or service-level characteristics varies by gender and can therefore be seen as potentially modifiable gender-specific predictors of treatment outcomes.
The findings of this review also underscore the point that merely changing a treatment program from mixed gender to women-only does not necessarily affect treatment outcomes for women with substance use disorders. Rather, we found that gender-specific treatment programming and interventions have been demonstrated to enhance treatment entry, retention, and outcomes among only certain subgroups of women with substance use disorders. A number of specific interventions focused on subgroups of women with substance use disorders have demonstrated feasibility and in some instances efficacy. These studies have often had small samples or have not yet benefited from a randomized controlled trial of the intervention, however. Additional research is needed to help design effective substance abuse treatment interventions for subgroups of women.
The state of our knowledge would benefit from Stage I trials of new therapeutic interventions focused on specific populations of women, as well as rigorous testing in randomized clinical trials of gender-specific interventions. Studies that compare gender-specific interventions in both women-only and mixed-gender programs would also be useful. In addition, existing studies indicate that certain combinations of treatment modalities (e.g., the addition of individual psychotherapy) or ancillary services (e.g., child care) improve treatment outcomes for women. Rigorous testing of these research questions for women and men would illuminate gender similarities and differences.
A comprehensive research agenda would include two major domains: (1) development and testing of effective treatment for specific subpopulations of women, and (2) randomized controlled trials testing the effectiveness of mixed-gender versus gender-specific treatments and treatment programs. For a number of subpopulations of women, there is a gap in the treatment research for the development and testing of effective treatments. These subpopulations include (a) older women with substance use disorders, especially those with alcohol and prescription drug use disorders, and (b) women with co-occurring substance use and eating disorders. There is also a dearth of research examining the interaction between gender and ethnicity in treatment process and clinical outcomes.
Finally, research on mixed-gender versus gender-specific treatments and treatment programs often has not been able to randomly assign patients or control for program or treatment-level characteristics. Future research should include: (a) a Stage II randomized controlled trial of a single standard substance abuse treatment approach (e.g., group drug counseling, relapse prevention) in single-gender male, single-gender female, and mixed-gender treatment groups; (b) investigation of gender-specific versus standard treatment content and the interaction of this content with different gender-specific groups; (c) identification of characteristics of women and of men who can benefit from mixed-gender versus single-gender treatments or treatment programs; and (d) cost-effectiveness of delivering single-gender versus mixed-gender treatments to different subgroups of women with substance use disorders.