Contingency management treatments are equally efficacious for both sexes in intensive outpatient settings.

Prevalence rates of substance use disorders are about double in men compared to women. In the National Epidemiologic Survey on Alcohol and Related Conditions sample, past year and lifetime rates of substance use disorders for men were 2.8% and 13.8%, respectively (Compton, Thomas, Stinson, & Grant, 2007). For women, these rates were significantly lower at 1.2% and 7.1%. Clinical course may vary by sex. Women tend to progress to disordered levels of use more quickly than men (Dawson, 1996; Hernandez-Avila, Rounsaville, & Kranzler, 2004; Lewis, Hoffman, & Nixon, 2014) and enter treatment at a younger age or more quickly relative to men (Bravo, Gual, Lligona, & Colom, 2013; Lewis & Nixon, 2014). Sex differences in comorbidities are also present. Women with drug use disorders are more likely to meet criteria for lifetime bipolar and alcohol disorders, and less likely to meet criteria for dependent and narcissistic personality disorders, than men after adjusting for socio-demographic characteristics (Goldstein, Dawson, Chou, & Grant, 2012). Related, psychiatric symptoms appear to be worse among women than men presenting to treatment (e.g., Grella, Scott, Foss, Joshi, & Hser, 2003; Green, Polen, Dickinson, Lynch, & Bennett, 2002). Women with substance use disorders also tend to be more disadvantaged than their male counterparts, with lower education levels, more unemployment, and more family problems than their male counterparts (Brady & Ashley, 2005; Goldstein et al., 2012; Najavits & Lester, 2008). Given the differences between sexes in the development and presentation of substance use disorders, increased attention has been given to the question of whether substance abuse treatment benefits both sexes equally. The data related to treatment outcomes, both in terms of treatment retention and abstinence outcomes, are mixed. While the bulk of studies find no differences in treatment retention (e.g., Devito, Babuscio, Nich, Ball, & Carroll, 2014; Green et al., 2002; Mertens & Weisner, 2000; Wong, Badger, Sigmon, & Higgins, 2002), others suggest that women have lower retention (Arfken, Klein, di Menza, & Schuster, 2001), are less likely to complete treatment (Arfken et al., 2001), and spend fewer days in treatment compared to men (Grella et al., 2003). Brady and Ashley (2005) examined treatment retention in a large nationally representative sample of patients with mixed substance disorders across multiple treatment settings, and both genders stayed in treatment for similar durations. Women were less likely to complete non-methadone outpatient treatment than men, but the relationship did not remain significant when controlling for confounds. Mertens and Weisner (2000) and Green et al. (2002) similarly found no sex differences in retention among outpatients with multiple substance use disorders. Three studies evaluated gender differences in clinical trials of patients with cocaine use disorders specifically. Devito et al. (2014) and Kosten et al. (1993) conducted pharmacotherapy trials, and Wong et al. (2002) evaluated patients from behavioral trials. None of these studies (Devito et al., 2014; Kosten, Gawin, Kosten, & Rounsaville, 1993; Wong et al., 2002) found a significant main effect of sex on treatment retention, and no interaction effects of sex by treatment condition were present in the two studies that examined these effects (Devito et al., 2014; Wong et al., 2002). Among the studies finding sex differences in treatment retention, Grella et al. (2003) examined outcomes among individuals in non-methadone programs and found that women spent fewer days in treatment compared to men for the index treatment episode. Arfken et al. (2001) similarly found that women seeking publically-funded treatment in non-methadone inpatient and outpatient settings were less likely to complete treatment (24% versus 46%) and had lower 30-day retention rates (62% versus 75%) compared to men. The opposite finding, that women have better treatment retention compared to men, has also been reported (Bravo et al., 2013; Choi, Adams, Morse, & MacMaster, 2015; Hser, Huang, Teruya, & Anglin, 2003; Hser, Huan, Teruya, & Anglin, 2004). Type of substance use disorder may also play a role in treatment outcomes. Individuals with substance use problems evidence poorer treatment retention compared to those with alcohol use problems (Brady & Ashley, 2005), but this relationship held only for women and not men in one study (Choi et al., 2015). Others find that these sex effects may be specific to certain substances, such as heroin and cocaine (Arfken et al., 2001). With respect to substance use outcomes, a mixed pattern of results also emerges. Some reports find equivalent outcomes for men and women (Hser et al., 2003; Garcia-Fernandez et al., 2011; Green, Polen, Lynch, Dickinson, & Bennett, 2004; Grella et al., 2003). Other studies suggest that women have poorer substance use outcomes (Aguiar, Neto, Lambaz, Chick, & Ferrinho, 2012; Archaryya & Zhang, 2003; Devito et al., 2014) and still others (Bravo et al., 2013; Weiss, Martinez-Raga, Griffin, Greenfield, & Hufford, 1997) find that women fare better in terms of reduced substance use or abstinence. Sex may interact with time in terms of treatment response in the first year beyond intake. Using a large mixed diagnosis treatment-seeking sample (N = 10,010) that included 96 inpatient, outpatient, residential, and methadone maintenance programs, Archaryya and Zhang (2003) found that women were significantly more likely to be classified as heavy or very heavy cocaine users at the 1-month in-treatment interview. However, these differences between men and women became smaller and nonsignificant over time through a 12-month follow-up. Collectively, these studies indicate mixed results in terms of the impact of sex differences on treatment outcomes. The present study examined sex effects of substance abuse treatment in general, and as relates to contingency management (CM) interventions specifically, using a combined sample from five randomized clinical trials (Petry, Alessi, Marx, Austin, & Tardif, 2005; Petry, Barry, Alessi, Rounsaville, & Carroll, 2012; Petry, Weinstock, & Alessi, 2011; Petry et al., 2004; Petry et al., 2006). CM is a behavioral intervention that uses tangible incentives to motivate behavior change. It is efficacious in reducing substance use across a range of substances, including cocaine, opiates, alcohol, nicotine, and marijuana, generating short-term effect sizes in the medium range, especially when appropriate parameters are applied (Benishek et al., 2014; Lussier, Heil, Mongeon, Badger, & Higgins, 2006; Prendergast, Podus, Finney, Greenwell, & Roll, 2006), and yielding the largest effect size of any psychosocial treatment for substance use disorders (Dutra et al., 2008). Meta-analyses (Benishek et al., 2014; Prendergast et al., 2006) suggest CM’s effects are sustained at least for short durations (e.g., 3-months) beyond the removal of the contingencies. Of the above reports, two studies (Garcia-Fernandez et al., 2011; Wong et al., 2002) examined sex effects in trials involving CM and only one of these examined sex by treatment condition interactions (Wong et al., 2002). Wong et al. (2002) examined sex differences in 188 cocaine dependent outpatients randomized to community reinforcement approach and contingent incentives or a comparison condition. They found that men and women had similar retention rates, reported similar reductions in cocaine use, and submitted similar rates of cocaine positive urinalysis results during treatment with no interactive effects with treatment condition. However, across treatment conditions, women reported more frequent cocaine use at intake and continued to report more days of cocaine use at each assessment through a 12-month follow-up. Another study (Garcia-Fernandez et al., 2011) examined sex as a predictor of end-of-treatment point prevalence abstinence in 50 cocaine dependent outpatients participating in two randomized clinical trials involving community reinforcement approach plus vouchers. Sex was not a significant predictor of cocaine abstinence. These reports suggest no sex effect in CM trials; however, both studies used small samples and may not have been powered to detect sex or sex by treatment condition interactions if present. This study therefore evaluated main and interactive effects of sex and treatment condition on substance use treatment outcomes using a sizable sample (N = 920). We hypothesized that women and men would differ on baseline characteristics including psychiatric symptoms but may respond equally well to treatment overall. We also evaluated whether sex interacts with treatment condition, such that women may benefit to a greater degree from CM interventions than men. This latter exploratory hypothesis is based on evidence that CM positively impacts psychiatric symptoms (Petry, Alessi, & Rash, 2013) and that women report greater psychiatric severity compared to men.