A review of research-supported group treatments for drug use disorders

This paper reviews methodologically rigorous studies examining group treatments for interview-diagnosed drug use disorders. A total of 50 studies reporting on the efficacy of group drug use disorder treatments for adults met inclusion criteria. Studies examining group treatment for cocaine, methamphetamine, marijuana, opioid, mixed substance, and substance use disorder with co-occurring psychiatric conditions are discussed. The current review showed that cognitive behavioral therapy (CBT) group therapy and contingency management (CM) groups appear to be more effective at reducing cocaine use than treatment as usual (TAU) groups. CM also appeared to be effective at reducing methamphetamine use relative to standard group treatment. Relapse prevention support groups, motivational interviewing, and social support groups were all effective at reducing marijuana use relative to a delayed treatment control. Group therapy or group CBT plus pharmacotherapy are more effective at decreasing opioid use than pharmacotherapy alone. An HIV harm reduction program has also been shown to be effective for reducing illicit opioid use. Effective treatments for mixed substance use disorder include group CBT, CM, and women’s recovery group. Behavioral skills group, group behavioral therapy plus CM, Seeking Safety, Dialectical behavior therapy groups, and CM were more effective at decreasing substance use and psychiatric symptoms relative to TAU, but group psychoeducation and group CBT were not. Given how often group formats are utilized to treat drug use disorders, the present review underscores the need to understand the extent to which evidence-based group therapies for drug use disorders are applied in treatment settings.

effectiveness trials, and other forms of systematic case studies and reviews) with clinical expertise and judgment to deliver treatment in the context of a patient's individual needs, preferences and culture. The shift towards EBP for substance use disorders has multiple benefits for practitioners and patients, including an increased focus on the implementation of treatments that are safe and cost-effective [14]. A recent survey of clinicians' practices with substance use treatment found that clinicians often conducted therapy in groups [15]. While most clinicians who completed the survey reported use of evidence-based treatment practices (EBT) some also reported the use of non-EBT practices [15]. Ensuring that clinicians can readily access information regarding the current state of evidence regarding group-based therapies for substance use disorders is critical for fostering increased use of EBTs.
Although any effort to summarize a literature as large and complex as the psychological treatment literature is useful, there are several limitations. With few exceptions, research-supported treatment lists categorize treatments by formal change theory (e.g., cognitive-behavioral, interpersonal) and describe little about the context, format, or setting in which treatments were conducted and tested [16]. As a result, it is often difficult to ascertain from existing resources whether research supported treatments were conducted in group or individual format. A group format is often used in substance use treatment [17] and aftercare programs [18][19][20][21][22]. The discrepancy between the wide-spread use of group therapy in clinical practice and the relative paucity of research on the efficacy of group treatments has been noted by treatment researchers [23] and clinicians [24]. According to Lundahl's [25] 2010 meta-analysis of studies evaluating the efficacy of motivational interviewing (MI), a commonly used treatment for substance use disorders, examination of the 119 studies concluded that studies of MI in a group format were too rare to draw solid conclusions about the efficacy of group MI. Also, it is possible that efficacy of treatments developed for individual delivery will be altered when delivered in a group format and vice versa. Given the limited empirical inquiry on group treatments for substance use, a framework organizing the literature on the efficacy of group therapy to treat substance use disorders would be useful. There is also a need for a more recent rigorous review of the empirical evidence to support group-based treatments for substance use disorders. Over 15 years ago, Weiss and colleagues conducted a review of 24 treatment outcome studies within the substance use disorder intervention literature comparing group therapy to other treatments conditions (i.e., no group therapy, individual therapy, group therapy plus individual therapy), and found no differences between group and individual therapy [26].
Given the importance of understanding the current evidence base for group-delivered treatments for substance use disorders, the present review sought to provide a summary of the literature on the benefits of group treatments for drug use disorders. Group treatments are potentially cost-effective, widely disseminable, and adaptable to a variety of populations but are lagging individual treatments in terms of research attention. Thus, highlighting characteristics of group treatments that are potentially efficacious is of import to stimulate further empirical inquiry. The review is organized by drug type (cocaine, methamphetamine, marijuana, opiate, mixed substance use disorders; SUD) and cooccurring SUD and psychiatric problems. We excluded studies focused on alcohol use disorder alone as this literature is summarized elsewhere (see Orchowski & Johnson, 2012). Given research suggesting that several factors impact outcomes of group treatments, including formal change theory driving the treatment approach (i.e., cognitive-behavioral, motivational interviewing), as well as patient factors [27], the review begins by first reviewing each theory of change (i.e., type of treatment), and then concludes by summarizing the research examining the extent to which patient factors influence the efficacy of group treatments for SUD.

Method
To locate studies that evaluated a group treatment for SUD that met review inclusion criteria, the authors conducted a comprehensive literature search of PsycINFO and MedLine through 2020. Three individuals then examined abstracts of the articles for relevance. In addition, the authors utilized the reference lists of review studies and meta-analyses of SUD-treatments to locate additional studies that might meet the review inclusion criteria. The authors and a research assistant then reviewed full articles with relevance to the current study and excluded any studies that did not meet the review inclusion criteria (see Fig. 1).
For inclusion in the review, studies needed to meet the following criteria: 1) report the findings of at least one group treatment; 2) provide at least one statistical comparison between the group treatment and a control condition; 3) randomize participants between the group treatment and control condition; 4) utilize a manualized treatment; 5) include patients with an interviewdiagnosed SUD; and 6) provide information regarding the demographic characteristics of the participants in the study. Studies' methods and results were used for data extraction. Studies which maintained a primary focus on the treatment of SUD, but also included treatment of a co-occurring psychiatric condition, were included in the review. Studies which included alcohol use as a comorbid diagnosis along another substance use were included. Studies examining the efficacy of group treatment for only alcohol use were excluded. The final set of articles included were 50 research studies that utilized a group treatment modality for the treatment of SUD, including separately examining cocaine, methamphetamine, marijuana, opioid, mixed substance, or SUD with comorbid psychiatric problems in adults.
It should be noted that several studies that met inclusion criteria were not reported in the present review because they did not report the use of a specific screening instrument for SUD as a part of the study inclusion/exclusion criteria. These studies are as follows and include these comparisons: group-based relational therapy [28] two studies by Guydish et al. [29,30] comparing a day treatment program to residential treatment (RT) program, a day treatment program to a coping skills group [31], standard care to a harm reduction group [32], 12 step group to a CBT group [33], medical management treatment (MMT) with CBT group to an MMT plus treatment reinforcement plan [34], treatment as usual to contingency management (CM) [35], professionally led recovery training group to treatment as usual (TAU) [36], two 4 month residential treatment programs [37], varying lengths of therapeutic community program (TPC) with and without relapse prevention [38], and Information and Referral plus peer advocacy to a Motivational group with CBT group [39].
Several treatment approaches are grounded in behavioral therapies and/or cognitive therapies. Broadly, cognitive therapy is an approach that focuses exclusively on targeting thoughts that are identified as part of a diagnosis or behavioral problem [28]. Cognitivebehavioral (CBT) therapy is an approach that targets specific symptoms, thoughts, and behaviors that are identified as part of a diagnosis or presenting problem [28]. Under the umbrella of CBT several other treatment modalities exist. For example, relapse prevention is a CBT treatment that hypothesizes that there are cognitive, behavioral, and affective mechanism that underlie the process of relapse [40]. Recovery training is a more specific form of relapse prevention, including education on addiction and recovery and reinforcing relapse prevention skills (e.g., understanding triggers, coping with cravings etc.) [41,42]. Other treatments focus on coping skills more broadly. For example, coping skills treatments include a focus on components of adaptability in interpersonal relationships, thinking and feeling, as well as approaches to self and life [28]. Some treatment approaches also recognize that individuals may not be ready to change their substance use. For example, motivational interviewing is often described as a therapy guiding technique in which the therapist is a helper in the behavior change process and expressed acceptance of the patient [43]. Standard group therapy includes 90 min sessions approximately twice a week in a group setting, [44] whereas intensive group therapy is a heavier dose of standard group therapy that includes 120-min sessions up to five times a week [44]. Psychoeducational therapy group focused on providing information on the immediate and delayed problems of substance use disorders to patients [45]. Lastly, dialectical behavior therapy (DBT) is a type of CBT therapy that focuses on helping regulate intense emotional states and provides skills to reduce arousal levels, and increase mindfulness, emotional regulation, and interpersonal skills [46]. Grounded within behavioral therapies, are behavioral skills training which focused on developing behaviors that are adaptive [28]. Contingency management is a type of behavioral therapy in which patients are reinforced or rewarded for positive behavioral change [47]. Harm reduction is a term for interventions aiming to reduce the problematic effects of behaviors [48]. Several treatment approaches also focus on interpersonal networks and building interpersonal skills. For example, social support is any psychological resources provided by a social network to help patients cope with stress [49]. Twelve-step facilitation group therapy is a more specific form of social support, which focuses on introducing patients to the 12 steps of alcoholics anonymous or related groups (i.e., cocaine or narcotics anonymous) to encourage 12-step meeting attendance in their community [33,50]. Seeking Safety is a present-focused and empowerment-based intervention focused on coping skills that emphasizes the importance of safety within interpersonal relationships [51]. Drug counseling describes treatment that aims to facilitate abstinence, encourage mutual support, and provide coping skills [52]. Finally, family therapy is a family-based intervention that aims to change, parenting behaviors and family interactions [53]. Overall, there are many overlapping components and skill sets in the models discussed above (See Table 1).

Group-based cocaine use treatments for adults
Nineteen studies were identified that targeted cocaine use and utilized some form of group therapy, the most of any drug in this review (see Table 2). Overall, the studies showed that all of the group therapy modalities included in this review generally reduced cocaine use when compared to treatment as usual (TAU), including day hospital groups [54]. Two studies, Magura et al. (1994) and Magura et al. (2002) did not find group differences between 8 months CBT and 8 months of TAU that consisted of methadone maintenance therapy among 141 patients with cocaine disorder [60,69]. When compared directly, individuals in CBT groups achieved longer abstinence than individuals in 12 step facilitation groups [33] or low intensity groups [64,65]. However, in another study, individuals with cocaine dependence receiving 12-step based Group Drug Counseling (GDC; similar to 12-step facilitation) had similar cocaine abstinence outcomes with or without additional individual CBT [41]. This may suggest that group 12step facilitation is an effective intervention for cocaine dependence. Two studies demonstrated the superiority of CM groups for reducing cocaine use as compared to   Cocaine use declined significantly from baseline to 4-and 12-month f/u across groups. CBT participants rated the quality of their counseling relationship higher and obtained more supportive services than TAU. Group was not associated with outcome.
Measures associated with poorer outcomes across both groups were: currently enrolled in methadone treatment, higher cocaine use frequency, greater cocaine use associated problem recognition, and an ambivalence toward methadone treatment.   [51]. Therefore, CBT group therapy and contingency management groups appear to be more effective at reducing cocaine use than TAU groups.

Group-based methamphetamine use treatments for adults
Only five treatment studies were identified that examined group treatments for methamphetamine use (see Table 3). Three studies found longer periods of abstinence for the group treatment (CM or drug+CM) than for TAU or non-CM conditions. The first study conducted by Rawson and colleagues compared matrix model (MM) with TAU in eight community outpatient settings [71]. The MM consisted of CBT groups, family education groups, social support groups, and individual counseling sessions along with weekly urine screens for 16 weeks. Participants in the MM condition attended more sessions, stayed in treatment longer, had more than twice as many contacts, evidence longer abstinence and greater self-reported psychosocial functioning relative to the TAU group. However, these significant differences did not persist 6 months later at follow-up. Shoptaw et al. (2006) [73] compared four groups for treating methamphetamine dependence sertraline + CM, sertraline only, placebo + CM, and placebo [73]. Additionally, all participants attended a relapse prevention group conducted three times a week over a 14-week period. Findings provided support for the efficacy of CM for amphetamine use disorders. Group treatment (CM or drug + CM) was more effective for sustaining longer periods of abstinence relative to TAU or non-CM conditions. Roll et al. [72] found that effects of CM relative to TAU became larger as the duration of CM increased. Jaffe et al. [70] evaluated a culturally tailored intervention for 145 methamphetamine dependent gay and bisexual males. Participants in the Gay Specific CBT condition reported the most rapid decline in levels of methamphetamine use relative to standard CBT, CBT + CM, suggesting benefits for culturally appropriate group methamphetamine interventions.

Group-based marijuana use treatments for adults
Two studies examining group treatments for adults with marijuana use disorders were identified (see Table 4). Both studies were conducted by the same research group, utilizing the same inclusion criteria for marijuana use (50 times in 90 days). The studies examined group relapse prevention (RP) [76], specifically designed for adult marijuana users. The first trial [75] (n = 212) comparing relapse prevention to a social support group found participants in both group treatment conditions did well overall, with two-thirds (65%) reporting abstinence of marijuana use for 2 weeks after session 4 or the quit date and 63% reporting abstinence during the last 2 weeks of treatment. Gender differences emerged; no differences between group treatments were found for women, but men in the relapse prevention group reported reduced marijuana use at the 3-month follow-up compared to men in the social support group.
A second trial [74] randomized participants to 14 sessions of group RP enhanced with cognitive behavioral skills training, two sessions of motivational interviewing (MI) with feedback and advice on cognitive behavioral skills (modeled after the Drinkers Check-up) [77], or a 4-month delayed treatment control (DTC) group which consisted of the RP group or individual MI treatment of the participants choosing. Compared to individuals randomly assigned to the DTC condition, participants in the group RP and individual MI conditions evidenced a significantly greater reduction in marijuana use and related problems over 16-month follow-up. However, examination of participants' reactions to DTC assignment indicated that participants who felt that changing their marijuana use was their own responsibility were more likely than those who did not to change their use patterns without treatment engagement.

Group-based opiate use treatments for adults
Five group treatment studies for opioid use were identified (see Table 5). Two studies compared the effectiveness of pharmacotherapy plus group therapies [79][80][81] to pharmacotherapy alone in samples of opioid dependent persons, and both found that adding group   ., control group). In contrast, a higher dose of group therapy provided without methadone maintenance was less effective for heroin use than was a lower dose of group therapy with methadone maintenance (Sees et al. [81]. This suggests that the combination of pharmacotherapy and group therapy for opioid use is optimal. Shaffer et al. [22] compared psychodynamic group therapy with a hatha yoga group. All participants received methadone maintenance and individual therapy. No differences between two treatment conditions were found. For all participants, longer participation in treatment was associated with reduction in drug use and criminal activity. Lastly, Des Jarlais et al. [78] compared a group social learning AIDS/drug injection treatment program (4 sessions, 60-90 min, over 2 weeks) to a control condition. All participants received information about AIDS and HIV antibody test counseling. Compared to control participants, intervention participants reported lower rates of drug injection over time.

Group treatments for mixed SUD for adults
Nine treatment studies were identified that targeted mixed substance use with group treatments (see Table 6). Three involved CBT. Downey et al. [82] compared group CBT plus individual CBT to group CBT plus vouchers in a sample of 14 polysubstance users (cocaine and heroin) maintained on buprenorphine. The study was significantly underpowered and they found no significant differences on treatment outcomes. Marques and Formiogioni [84] compared individual CBT to group CBT in a sample of 155 participants with alcohol and/or drug dependence. They found that both formats resulted in similar outcomes, with higher compliance in the group CBT participants (66.7% compliance with treatment). Rawson et al. [87] compared three 16-week treatments: CM, group CBT, and CM plus group CBT, among 171 participants with cocaine disorder or methamphetamine abuse. They found that CM produced better retention and lower rates of stimulant use than CBT during   Two studies involved Group Drug Counseling (GDC). Greenfield et al. [52] compared a group drug counseling (GDC) (mixed gender) to a women's recovery group (WRG) that both met weekly, for 12 weeks, for 90-min sessions among 44 participants that had a substance use disorder other than nicotine. WRG evidenced significantly greater reductions in drug and alcohol use over the follow up compared with GDC. Schottenfeld et al. [88] compared GDC (weekly, 1-h group sessions) to a community reinforcement approach (CRA; twice weekly sessions for the first 12 weeks and then weekly the following 12 weeks) among 117 patients with an opioid and cocaine use disorder. There were no differences in retention or drug use.
Remaining studies examined other interventions. Margolin et al. [83] compared an HIV Harm reduction program (HHRP) that met twice weekly for 2 h to an active control group that met six times in a sample of 90 HIV-seropositive methadone-maintained injection drug users with opioid dependence, and abuse or dependence on cocaine. At follow up, they had lower addiction severity scores and were less likely to have engaged in high risk behaviors compared to control. McKay et al. [85] compared weekly phone monitoring and counseling plus a support group in the first 4 weeks (TEL), twice-weekly individualized relapse prevention, and twice-weekly standard group counseling (STND) among 259 referred participants with alcohol use disorder or cocaine disorder. STND resulted in more days abstinent than TEL. Nemes et al. [86] compared a 12-month group program (10 months inpatient and 2 months outpatient) to an abbreviated group program (6 months inpatient, 6 months outpatient) among 412 patients with multiple drug/alcohol use disorders. Results indicated that both groups had ETP evidenced enhanced abstinence rates at 3-month and 12-month follow-up compared to STP, regardless of type of drug use. a DSM criteria used unless otherwise noted. b RAAT Random Assignment to Active Treatment, RAWC Random Assignment with Control, PPWC Pre-Post with Comparison Group (matched or otherwise). c AD Alcohol Dependence, CD Cocaine Dependence, SUD Substance Use Disorder. Articles included in the review utilized interview diagnosed screening materials (i.e., SCID) to identify drug abuse or dependence. Articles included in this table utilized a control group reduction in arrests and drug use. There were no significant difference between groups. Lastly, Smith et al. [89] compared a standard treatment program (STP, daily group counseling, family outreach, 12-step program introduction, four 2 h sessions for family) to an enhanced treatment program (ETP; twice weekly group on relapse prevention and interpersonal violence in additional to all STP components) among 383 inpatient veterans meeting for an alcohol, cocaine, or amphetamine use disorder. Results indicated that ETP had enhanced abstinence rates at 3-month and 12-month follow up compared to STP, regardless of type of drug use.

Group Treatments for SUD and Co-Occurring Psychiatric Problems
Individuals with psychiatric distress are at high risk for comorbid SUD [90]. Ten randomized controlled studies meeting our inclusion criteria examined the efficacy of group therapy for SUD and co-occurring psychiatric problems (see Table 7). Three studies described group treatment of SUD and co-occurring DSM-IV Axis II disorders [18,91,96], three studies examined group treatment of drug abuse and co-occurring DSM-IV classified Axis I disorders [92,93,99], one study explored group drug abuse treatment and co-occurring psychiatric problems among homeless individuals without limiting to DSM-IV Axis I or Axis II diagnoses [97], and one study focused on group drug treatment among individuals testing positive for HIV [98]. Within this diverse set of RCTs, participants generally included individuals diagnosed with any form of SUD; however, some studies focused specifically on individuals using cocaine [91,97] or cocaine/opioids [98]. A range of group treatment approaches are represented, including group psychoeducational therapy, group CBT approaches, group DBT, Seeking Safety and CM. DiNitto and colleagues [92] evaluated the efficacy of adding a group-based psychoeducational program entitled "Good Chemistry Groups" to standard inpatient SUD treatment services among 97 individuals with a dual diagnosis of SUD and a DSM-IV Axis I psychological disorder. The nine 60-min Good Chemistry Group sessions were offered 3 times per week for 3 weeks. When compared to standard inpatient treatment, the addition of the psychoeducational group was not associated with any changes in medical, legal, alcohol, drug, psychiatric or family/social problems among participants.
The efficacy of adding a psychoeducational group treatment to standard individual therapy to address HIV risk among cocaine users has also been examined [91]. Participants were randomly assigned to complete the following: 1) individually-administered Standard Intervention developed by the NIDA Cooperative Agreement Final Cohort sites [100] including HIV testing, and preand post-HIV testing counseling on risks relating to cocaine use, transmission of STDs/HIV, condom use, cleaning injection equipment, and the benefits of treatment; or) Standard Intervention plus four 2-h peerdelivered psychoeducational groups addressing stress management, drug awareness, risk reduction strategies, HIV education and AIDS. Among the sample of 966 individuals completing the 3-month follow-up, the group psychoeducational treatment was not differentially effective in reducing drug use and HIV risk behavior in comparison to standard treatment alone at 3-months post-baseline, regardless of treatment type, individuals with antisocial personality disorder (ASPD) demonstrated less improvement in crack cocaine use compared to individuals without ASPD or depression.
The following types of group CBT have sustained research evaluation meeting our inclusion criteria to address co-occurring SUD and Axis I or Axis II disorders: 1) group behavioral skills training; 2) group cognitive behavioral therapy; 3) group-based Seeking Safety [51], and 4) group dialectical behavioral therapy. Specifically, Jerrell and Ridgely [93] examined the efficacy of group behavioral skills (BS) training, group-based 12-step facilitation (TS) treatment, and intensive case management among 132 individuals with a dual diagnosis of SUD and another Axis I psychiatric problem over the course of 24-months. Based on the Social and Independent Living Skills program [101], the BS group included one group per week addressing self-management skills designed to enhance abstinence, including medication management, relapse prevention, social skills, leisure activities and symptom monitoring. Relative to participants in TS groups, participants in the BS groups evidenced increased psychosocial functioning and decreased psychiatric symptoms (i.e., schizophrenia, depressive symptoms, mania, drug use and alcohol use) across the 6-, 12-and 18-month follow-up assessments after treatment entry.
Lehman and colleagues' [95] examination of the efficacy of group CBT for substance abuse compared to TAU among 54 individuals with SUD and either schizophrenia or a major affective disorder revealed no differences between treatment groups over the course of a 1-year follow-up period. More promising findings were reported in Fisher and Bentley's [18] evaluation of a group CBT and group therapy based in the disease and recovery model (DRM) among 38 individuals with dual diagnosis of SUD and a personality disorder. Groups met three times per week for 12 weeks and were compared to TAU. Individuals in group CBT and group DRM indicated improved social and family functioning compared to TAU, and among those who completed the group in an outpatient setting, CBT was more effective in reducing Group behavioral therapy plus abstinence contingent housing and work administered in the context of a day treatment program was compared to behavioral group treatment alone among individuals with cocaine abuse/ dependence, non-psychotic psychiatric conditions, and homelessness [97,102]. The group behavioral therapy included 8 weeks of daily treatment (4 h and 50 min per day) of groups addressing relapse prevention training, assertiveness training, AIDS education, 12-step facilitation, relaxation, recreation development, goal setting, and goal planning. Participants also engaged in a process-oriented group as well as individual counseling and urine monitoring and engaged in a weekly 90 min psychoeducational group therapy during months 3-6 following treatment enrollment. Individuals who received contingency-based work and housing were provided with rent-free housing and employment in construction or food service industries after 2 consecutive weeks of abstinence [103]. Relative to BS groups alone, group behavioral day treatment plus contingency management was associated with greater abstinence at 2-and 6-month follow-ups [102] and were less likely to relapse [97], although gains were not maintained at 12-  [104]. Both groups evidenced positive changes in drug use overtime compared to baseline [104]. Zlotnick, Johnston and Najavits [99] evaluated the efficacy of Seeking Safety (SS), in comparison to treatment as usual (TAU) among 49 incarcerated women with substance use disorder (SUD) and full or subthreshold posttraumatic stress disorder (PTSD). SS aims to decrease PTSD and SUD through psychoeducational and presentfocused and empowerment-based instruction on coping skills that emphasize abstinence and safety [51]. The SS group treatment included 90-min group sessions held three times per week, that were completed in addition to the 180 to 240 h of group and individual therapy provided in TAU. All participants showed similar improvement on assessments of PSTD, SUD, legal problems and other psychiatric concerns at 12-week, 3-and 6-month follow-ups following prison release. Nonetheless, there was a trend for improved PTSD and continued improvements in psychiatric symptoms at follow-up among participants completing SS compared to TAU. Greater completion of SS sessions was associated with increased improvement in PTSD as well as drug use among women [99].
Dialectical behavioral group therapy (DBT), a CBTfocused treatment for individuals with borderline personality disorder (BPD), has also been evaluated in comparison to TAU among individuals with BPD and cooccurring SUD [96]. Core elements of DBT are manualized [105], and have been evaluated in prior research [106][107][108]. Techniques center on providing the participant with acceptance and validation while maintaining a continual focus on behavior change, and include the following: mindfulness skills training, behavioral analysis of dysfunctional behavior, cognitive restructuring, coping skills training, exposure-based strategies addressing maladaptive emotions, and behavioral management skills training. DBT was administered through 2 ¼ hour weekly group sessions administered in combination with 60 min of weekly individual therapy and the opportunity for skills-coaching phone calls. Relative to TAU, participants randomly assigned to DBT demonstrated greater reductions in drug use during the 12-month treatment and at the 16-month follow-up assessment, as well as greater gains in adjustment at the 16-month follow-up assessment.
Although contingency management is commonly administered individually, Petry and colleagues [98] examined the efficacy of weekly 60-min group-based contingency management (CM) for reinforcing health behaviors and HIV-positive individuals with cocaine or opioid disorders (N = 170) in comparison to 12-step facilitation (TS) over the course of a 24-week period. Overall, participants in CM were more likely than those in TS to submit consecutive drug-free urine specimens, although the overall proportion of drug-free specimens did not vary between groups during treatment or over the follow-up period. Notably, during treatment, group CM was associated with greater reductions in HIV-risk behaviors as well as overall viral load compared to TS; although effects were not maintained over the follow-up period.
Across these studies, many trials showed positive gains for both group treatments examined [18,97,98], or no difference between groups when examining the benefit of adding group treatment to existing TAU [91,92,95,99]. However, one study demonstrated greater reductions in drug use among individuals with BPD and SUD who completed group DBT in comparison to TAU [96]. Further, BS groups were more effective than TS groups in improving psychosocial functioning and decreasing substance use [93]. Finally, CBT was more effective than DRM in reducing alcohol use, enhancing psychological functioning and improving social and family functioning compared to DRM and TAU among individuals dually diagnosed with SUD and a personality disorder [18].

Factors associated with treatment efficacy Gender and treatment efficacy
Five of the studies included in the present review examined whether treatment was differentially effective for men and women. Although Jarrell and Ridgely's [93] evaluation of group BS, group TS and individual case management for individuals with SUD and co-occurring Axis I disorders did not examine whether group treatment types were differentially effective for men and women, data indicated that women-regardless of treatment group-reported higher role functioning (i.e.., independent living, work productivity, as well as immediate and extended social relationships), increased psychiatric symptomatology (depression, mania, drug use, alcohol use) across the follow-up periods compared to men.

Race and ethnicity and treatment efficacy
Among the studies included in the present review, only three examined whether treatment efficacy varied as a function of race and ethnicity. A secondary examination of the efficacy of group BS in comparison to group TS and individual case management [93] suggested that outcomes in each group treatment among ethnic and racial minority clients were equivalent to White participants during the 6-month follow [94]. The initial evaluation indicated that-regardless of group treatment type-racial/ethnic minority participants reported lower scores in personal well-being, lower life satisfaction (i.e., satisfaction with living), worse role functioning (i.e., independent living, work productivity, immediate and extended social relationships) over the follow-up periods compared to White participants [93].

Conclusions
In general, participants in group treatment for drug use disorders exhibit more improvement on typical measures of outcome (e.g., abstinence & use rates, objective measures, urinalysis) when compared to standard care without group [18,109] and those who refuse or drop out of treatment [110]. Specifically, CBT and CM appear to be more effective at reducing cocaine use than TAU groups. CM is effective in increasing periods of abstinence among users of methamphetamine. Both relapse prevention and social support group therapy were effective for marijuana use although relapse prevention was more helpful for men than for women. Brief MI and relapse prevention were both effective at reducing marijuana use. CBT and CBT-related treatments (including the matrix model) when added to pharmacotherapy were more effective for opioid use disorder than pharmacotherapy alone. Effective treatments for Mixed SUD include group CBT, CM, and women's recovery group. Longer relapse prevention periods appear to be more helpful in reducing mixed SUD. Behavioral skills and behavioral skills plus contingency management helped decreased psychiatric symptoms and drug use behaviors. Psychoeducation groups alone, a commonly used intervention, were not effective at addressing SUD and co-occurring psychiatric problems. Additionally, it is important to note that there is potential for risk of bias in the studies included across four domains: participants, predictors, outcome, and analysis [111]. The current study did not comprehensively assess for risk of bias and this is a study limitation. Future research could assess for risk of bias by following the guidelines suggested by the Cochrane Handbook [112].
The current literature offers a wide variety of group treatments with varying goals and based on varying formal change theories. Overall, studies that reported between-group effect size (n = 7) reported small to medium effect sizes potentially suggesting differences were moderate but of potential theoretical interest. Of those seven studies, only two studies reported large effect sizes (both comparing an active treatment to a delayed treatment/untreated condition). In order to better characterize magnitude of intervention effects, future studies should report effect sizes and their confidence intervals [113,114]. Moreover, groups based on cognitive-behavioral theory [35], motivational enhancement theory [43], stages of change theory [115], 12-step theory [41] and psychoeducational group models [116] have all been the subject of recent studies. Steps of treatment have also been used to classify groups for acutely ill individuals with SUD versus middle stage (recovering) or after care groups, with the latter mainly focusing on relapse prevention. Group therapy is providedat least as an augment to multimodal interventionsin most of the outpatient and inpatient programs in English speaking and European countries [17,117]. Therefore, continued efforts to implement and scale up group-based treatments for SUD known to be effective are needed. CM appears to be effective at addressing various drug use problems and further research should evaluate whether it would also be useful for marijuana use.

Future Research Questions
Studies of other group treatments for SUD that use rigorous, interview-based diagnosis, use control groups, randomly assign participants to condition, report the ethnic and racial composition of the sample, are adequately powered, implement a treatment manual, and compare outcomes to individual treatment as well are necessary. Little is known regarding the possible mediators and moderators of treatment outcome in group interventions for SUD

Key Learning Objectives
Group treatment approaches are widely utilized and are often less costly to implement than individual treatments, currently we know very little whether one group approach is superior to another in the treatment of SUD. Group treatment approaches seem to be more effective at improving positive outcomes (e.g., abstinence, use rates, objective measures, urinalysis) when compared to standard care without group [18,109], and those who refuse and drop out of treatment More thorough randomized controlled trials of group SUD treatments are needed [110].