Substance abuse and criminality among youth in Sweden are urgent problems. More knowledge on effective interventions is crucial to help vulnerable youth at risk of developing an array of severe problems affecting both themselves, their relatives and society (Grahn, Lundgren Chassler \& Padyab, 2015). Effective help for substance abuse increases chances to abandon criminality and build up a constructive life (Henderson et al, 2016, Chermack et al, 2010). Youth with severe substance abuse and psychosocial problems, such as criminal and socially disruptive behavior, often receive treatment in compulsory institutional care. The responsible party for delivering care in this domain is The Swedish National Board of Institutional Care, (Statens institutionsstyrelse, SiS). SiS provides institutional care on basis of the Swedish laws Care of Young Persons (Special Provisions) Act, LVU, Care of Substance Abusers (Special Provisions) Act, LVM, Secure Youth Care Act, LSU. Treatment is delivered in lockable institutions, situated in different locations around the country. However, the institutional setting differs from standard outpatient care where most substance use treatments have been designed for. For example, the locked ward and security routines pose challenges when fostering pro-social and constructive behavior (Gevers, Poelen, Scholte, Otten \& Koordeman, 2020). Every activity must be thoroughly planned to lower risks of violence or escaping and routines, such as visitations, can lower the ability and motivation to engage in positive activities outside the institution (Brauers, Kroneman, Otten, Lindauer \& Popma, 2016). The Swedish Agency for Health Technology Assessment and Assessment of Social Services, SBU, concluded in a systematic review (2016) that the scientific support for several of the treatment programs conducted at SiS are inadequate. Consequently, that more research on treatment in institutional care is needed, especially high-quality studies with a study design adjusted to the specific conditions prevailing there.

An empirically supported substance use treatment developed for youth ages twelve to twenty five is the Adolescent Community Reinforcement Approach, A-CRA. A-CRA promotes long-term abstinence, increase social stability and decrease depression and other co-morbid psychiatric problems according to a large number of studies since the nineteen seventies (Azrin, Sisson, Meyers, \& Godley, 1982; Dennis et al., 2004; Hunt \& Azrin, 1973; Godley et al., 2014; Godley et al., 2001; Godley, Smith, Passetti, \& Subramaniam, 2014). A-CRA is recommended in national guidelines for the treatment of substance use disorder in adolescents (Socialstyrelsen, 2017). Treatment consists of eighteen procedures that aim to reduce problematic behaviors and increase constructive behaviors. Example of procedures are happiness scale and treatment goals, functional analysis of substance use behavior, increasing prosocial activities, drink/drug refusal, relapse prevention, communication skills, caregiver sessions, job seeking skills and anger management (Godley, Smith, Myers \& Godley, 2016). Procedures are combined and tailored to youth individual goals and needs (Godley et al., 2016). A-CRA has also proven helpful for justice-involved youth with substance use disorder under probation (Henderson et al. 2016) and for homeless youth (Slesnick et al., 2007). However, as many other psychological treatments, A-CRA has mostly been delivered and evaluated within outpatient care. It is unclear whether A-CRA is as effective when delivered in compulsory care where many adolescents with severe substance use disorder and criminal behavior receive treatment.

The overall objective of this research project is to scientifically evaluate the effectiveness of A-CRA in compulsory institutional care for youth with substance use disorder and criminal behavior. In addition, to explore mechanisms of change, what mediates substance abuse and criminal behavior.

Youth are randomized to either treatment as usual or treatment as usual with the addition of A-CRA. Treatment as usual is defined as the interventions and treatments adolescents are usually offered and undergo in institutional care. These are Motivational Interviewing, MI, Cognitive Behavioral Therapy, CBT, Aggression Replacement Therapy, ART or Acceptance and Commitment Therapy, ACT. Randomization takes place at site level with even allocation to the groups. Quantitative measurements take place before, during and after treatment as well as follow-up at 1, 3, 6 and 12 months. Primary endpoint is 6 months after treatment completion. Qualitative data will be collected by interviewing participants at 3 month follow-up. Potential adverse events will be collected after treatment completion using open questions and registered when reported by staff in the research group or at KI.