Review
Substance abuse treatment entry, retention, and outcome in women: A review of the literature

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Abstract

This paper reviews the literature examining characteristics associated with treatment outcome in women with substance use disorders. A search of the English language literature from 1975 to 2005 using Medline and PsycInfo databases found 280 relevant articles. Ninety percent of the studies investigating gender differences in substance abuse treatment outcomes were published since 1990, and of those, over 40% were published since the year 2000. Only 11.8% of these studies were randomized clinical trials. A convergence of evidence suggests that women with substance use disorders are less likely, over the lifetime, to enter treatment compared to their male counterparts. Once in treatment, however, gender is not a significant predictor of treatment retention, completion, or outcome. Gender-specific predictors of outcome do exist, however, and individual characteristics and treatment approaches can differentially affect outcomes by gender. While women-only treatment is not necessarily more effective than mixed-gender treatment, some greater effectiveness has been demonstrated by treatments that address problems more common to substance-abusing women or that are designed for specific subgroups of this population. There is a need to develop and test effective treatments for specific subgroups such as older women with substance use disorders, as well as those with co-occurring substance use and psychiatric disorders such as eating disorders. Future research on effectiveness and cost-effectiveness of gender-specific versus standard treatments, as well as identification of the characteristics of women and men who can benefit from mixed-gender versus single-gender treatments, would advance the field.

Introduction

Among the most reproducible findings of studies focusing on women and substance use disorders is that of the heightened vulnerability of women to the adverse medical and social consequences of substance use, abuse, and dependence (Chatham et al., 1999, Gentilello et al., 2000, Henskens et al., 2005, Hernandez-Avila et al., 2004, Kosten et al., 1985). For substance use disorders, including alcohol, opioid, and cannabis dependence, females advance more rapidly from use to regular use to first treatment episode than do their male counterparts (Dawson, 1996, Hernandez-Avila et al., 2004, Johnson et al., 2005, Orford and Keddie, 1985, Piazza et al., 1989, Randall et al., 1999). In addition, when they enter treatment, in spite of fewer years of use and smaller quantities of substances used, their substance abuse symptom severity is generally equivalent to that of males (Hernandez-Avila et al., 2004, Piazza et al., 1989, Randall et al., 1999). Even with fewer years of substance use, at treatment entry, females average more medical, psychiatric, and adverse social consequences of their substance use disorders than males. Given the approximate equivalency of age of initiation of substance use between males and females in the younger age cohorts (Hernandez-Avila et al., 2004, Holdcraft, 1999, Holdcraft and Iacono, 2002, Holdcraft and Iacono, 2004, Johnson et al., 2005), this heightened vulnerability of females of all age cohorts gives rise to particular clinical and public health concerns (Greenfield, 2002). It also sets the stage for examining the information on predictors of treatment entry, retention, and outcomes for women with substance use disorders.

Until the early 1990s, the substance abuse treatment literature was based primarily on male samples, or mixed samples of men and women without any focus on gender differences. Women were excluded from most studies due to their childbearing potential. As a result, findings about effective substance abuse treatments were not fully generalizable to women.

In 1993, US government guidelines highlighted the importance of expanding research to include women of childbearing potential (FDA, 1993) and in 1994, the U.S. National Institutes of Health (NIH) published its “NIH Guidelines on the Inclusion of Women and Minorities as Subjects in Clinical Research” (FDA, 1994) (Mathias, 1995, NIDA, 1999). Since these guidelines were issued, the number of published research reports examining substance abuse treatment for women has increased annually in the U.S. The goal of this report is to review systematically and critically the information from the available research literature, focusing on reports published in the period from 1990 to 2005. We examine specific characteristics associated with substance abuse treatment outcomes for women in the context of three stages of the substance abuse treatment process: (1) entry, (2) retention, and (3) post-treatment substance abuse outcomes. In order to set these results in context, the literature search that informed this critical review examined published English-language studies from 1975 to 2005. We also included literature reviews, meta-analyses, and theoretical papers. The results of our search of the literature from 1975 to 2005 are included in table format and can be found by accessing the online version of this paper and Supplementary Material (see Appendix A for more information).

Because this paper focuses on treatment outcomes, we excluded studies of general characteristics and epidemiology of women with substance use disorders that have been reported and reviewed elsewhere (Back et al., 2003, Brennan et al., 1993, Bulik et al., 2004, Grant et al., 1996a, Grant et al., 1996b, Greenfield et al., 2002, Hanna and Grant, 1997, Holdcraft and Iacono, 2004, Pelissier and Jones, 2005, Regier et al., 1990). Previous reviews of the literature on women and substance abuse treatment outcomes have generally focused on gender differences and included studies of mixed-gender samples (Brady and Randall, 1999, Lex, 1991, Pelissier and Jones, 2005, Sinha and Rounsaville, 2002, Toneatto et al., 1992), or have focused on outcomes in women without a gender comparison (Ashley et al., 2003, Orwin et al., 2001). Because this review focuses on treatment outcomes for women with substance use disorders, it includes both studies that utilized women-only samples and studies involving gender comparisons reported in mixed-gender samples.

The present review focused on adult women and does not report on treatment outcomes in female adolescents, which are reviewed elsewhere (National Center on Addiction and Substance Abuse (CASA), 2003). While studies focusing on substance abuse treatment outcomes in pregnant women are included in the supplementary materials, a full review of treatment outcomes among pregnant women is beyond the scope of this report; several recent reviews of this topic exist (Brady and Ashley, 2005, Finkelstein, 1994, Greenfield and Sugarman, 2001, Grella, 1996, Grella, 1997, Howell et al., 1999). Similarly, studies of gender differences in treatment outcomes among criminal justice populations have been reviewed elsewhere (Langan and Pelissier, 2001, Pelissier, 2004, Pelissier et al., 2003) and are not included in this review. In addition, while nicotine dependence is a major public health problem among women, it is most often treated in clinical settings (e.g., primary care and other general medical care) (Ockene, 1998, Shin, 1997) that are separate from substance abuse treatment programs. Reviewing the outcomes of these nicotine treatment studies is beyond the scope of this review. Finally, this report excluded studies in which substance abuse outcomes were secondary outcomes (e.g., studies of HIV in which HIV outcomes were primary).

Using Medline and PsycInfo databases, we searched for articles published between January 1975 and September 2005. We included the following search terms and subject headings: alcohol abuse, alcoholism, alcohol drinking, drug abuse, drug dependency, opioid-related disorders, substance abuse, substance dependence, substance-related disorders, outcome, predictor, retention, gender, female, sex, human females, human sex differences, sex factors, women, substance abuse treatment, treatment, treatment entry, treatment outcomes, outcome predictor, treatment retention, outcome, predictor, retention, outcome and process assessment, cohort studies/prospective studies, therapeutics, client characteristics, and demographic characteristics. In order to eliminate non-relevant articles, search of the PsycInfo database restricted the eligible field for the search to “subjects” or headings under which PsycInfo indexed each article. The search focused on English language literature only. The search was sensitive to the specific terms we entered and may have missed articles not categorized by these key words.

All substances except nicotine were reviewed. We also reviewed the reference lists of these articles to search for publications that did not appear in the search described above.

Using these methods, 2,474 articles from Medline and 636 articles from PsycInfo were found. Titles and abstracts were reviewed by three of the authors (S.F.G., R.K.M., and M.L.) for relevance, and articles that were not relevant to the topic or met any of the exclusion criteria were eliminated. There were then 280 relevant articles, 90% of which were published in 1990 or later; of those, 43.9% were published since the year 2000.

Only 11.8% of all studies reviewed were randomized clinical trials. An additional 7.9% were non-randomized or quasi-experimental trials. The most frequently occurring type of article (31.2%) reported on studies that used the prospective cohort design, in which a population was followed naturalistically and assessed to determine clinical outcomes.

Results of the literature search by study type and reported results (1975–2005) are presented in the online supplementary materials. This review discusses the results from 1990 to 2005, focusing on studies that used randomized clinical trial, non-randomized clinical trial, quasi-experimental, or naturalistic study designs. We review characteristics associated with treatment entry, retention, and substance abuse treatment outcomes in women. We then examine substance abuse treatment outcomes for women in single-gender versus mixed-gender approaches. Finally, we discuss and summarize our findings and present implications for a research agenda on the role of gender in substance abuse treatment outcomes.

Section snippets

Gender disparities among participants in substance abuse treatment

Many studies have reported the relatively low proportion of women in substance abuse treatment programs (Brady and Ashley, 2005, Pelissier and Jones, 2005, Schober and Annis, 1996, Weisner, 1993, Weisner and Schmidt, 1992) compared with the prevalence of these disorders among women in the general population. For example, in 1991 the ratio of men to women was 3.3:1 in alcohol treatment facilities (Dawson, 1996), while the male to female ratio of alcohol use disorders in the population for that

Characteristics associated with substance abuse treatment retention and completion

Longer substance abuse treatment episodes and successful completion of treatment are usually related to positive outcomes, but as many as 50% of patients in drug and alcohol treatment drop out of treatment within the first month (Stark, 1992). A comparison of research on predictors of treatment retention and completion is difficult due to the diverse ways in which these concepts have been defined. Retention in treatment has been defined as a dichotomous variable, such as attendance for a

Substance abuse outcomes versus predictors of outcomes

While concerns have been raised about the effectiveness of substance abuse treatment for women (Ferrence, 1994, Floyd et al., 1996, Hodgins et al., 1997, Schmidt and Weisner, 1995, Schober and Annis, 1996), many studies have found few or no gender differences in treatment outcome across various populations (e.g., Acharyya and Zhang, 2003, Alterman et al., 2000, Ballesteros et al., 2004, Benishek et al., 1992, Foster et al., 2000, Green et al., 2004, Greenfield et al., 1998, Hser et al., 2003,

Gender-specific versus mixed-gender treatment services

Many programs have developed gender-specific and gender-sensitive programs and services for women, but the effects of these changes on treatment outcomes remain unclear (LaFave and Echols, 1999, Nelson-Zlupko et al., 1995, Schliebner, 1994, Smith and Weisner, 2000, Wilke, 1994). A meta-analysis examining effectiveness of single-gender substance abuse treatment for women (Orwin et al., 2001) concluded that single-gender treatment was effective, but that its strongest impact was on pregnancy

Summary of findings and implications for research on gender differences and substance abuse treatment outcomes

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

Acknowledgements

The authors gratefully acknowledge the support of the Gender Special Interest Group of the Clinical Trials Network.

The authors also acknowledge Martha Swain for her assistance in editing the manuscript and Megan Ghiroli, Melissa Gordon, and Andrea Hegedus for their contributions to early stages of the manuscript. This publication was supported by a series of grants from NIDA as part of the Cooperative Agreement on the National Drug Abuse Treatment Clinical Trials Network (CTN). Northern New

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    A table listing the results of our search can be found by accessing the online version of this paper and Supplementary Material. Please see Appendix A for more information.

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