This study aims to compare the Italian and U.S. forensic models in the treatment of offenders with dual diagnosis through a three-year longitudinal design. In Italy, the closure of Judicial Psychiatric Hospitals following Law 81/2014 led to the establishment of a community-based forensic system centered on REMS (Residences for the Execution of Security Measures), integrated within the National Health Service. This model seeks to limit institutionalization and promote rehabilitative pathways in community settings. However, it continues to face challenges related to limited bed availability, waiting lists, and the complex management of social dangerousness. In contrast, the U.S. system, particularly in California, is characterized by high-security forensic psychiatric hospitals with large capacities, but also presents issues such as prolonged hospitalizations, an aging patient population, and a high prevalence of substance use disorders.

Dual diagnosis, defined as the co-occurrence of psychiatric disorders and substance use disorders, is highly prevalent in forensic populations and is associated with increased clinical complexity, higher risk of recidivism, and poorer treatment outcomes. Neurobiological and psychological mechanisms underlying addiction-including dysfunctions in the dopaminergic reward system, craving processes, and impairments in executive functioning-contribute to reduced behavioral control and increased impulsivity. Theoretical models such as the self-medication hypothesis and multifactorial frameworks suggest that substance use may both exacerbate psychiatric symptoms and represent an attempt to regulate them.

Given these complexities, integrated treatment approaches that combine psychiatric care and addiction interventions are essential, particularly in forensic settings. The present study includes offenders with mental illness in forensic care systems in Italy and California, encompassing both custodial and non-custodial settings. Participants will be followed over a three-year period, with assessments conducted at 12, 24, and 36 months. The methodology involves the use of standardized instruments to evaluate psychopathological severity, global functioning, risk of violent recidivism, protective factors, treatment adherence, impulsivity, and substance use. Data on clinical outcomes, antisocial behaviors, and discharge conditions will also be collected.

The primary objectives of the study are to describe and compare the clinical, demographic, and criminological profiles of forensic populations with dual diagnosis; to examine treatment pathways and outcomes; to identify indicators of treatment effectiveness; and to evaluate both risk and protective prognostic factors, as well as their predictive value for recidivism and clinical trajectories.

The expected impact of the study lies in improving the understanding of differences between community-based and hospital-based forensic models, with the goal of identifying integrated strategies capable of enhancing rehabilitation, reducing recidivism, and improving long-term outcomes. Findings may contribute to the development of more effective and individualized treatment approaches, as well as inform health and judicial policies aimed at better integrating clinical care and risk management in dual diagnosis forensic populations.

Inclusion Criteria:

• Adults aged 18 years or older.
• Individuals admitted to forensic psychiatric care in Italy or California.
• Presence of a diagnosed mental disorder according to DSM-5 / ICD criteria.
• Presence of a current or lifetime Substance Use Disorder, consistent with a dual-diagnosis condition.
• Placement in one of the study settings:

Italy: REMS or other forensic/community facilities under custodial or non-custodial security measures; California: Department of State Hospitals forensic facilities.

• Ability to provide written informed consent, or consent provided through a legal guardian when applicable.
• Availability for longitudinal follow-up at 12, 24, and 36 months.

Exclusion Criteria:

• Absence of a confirmed psychiatric disorder.
• Absence of current or lifetime Substance Use Disorder.
• Non-forensic psychiatric patients without criminal justice involvement.
• Severe cognitive impairment or neurological condition preventing valid assessment.
• Acute medical or psychiatric instability that makes participation temporarily impossible.
• Inability to complete the assessment procedures, even with support or adapted administration.
• Refusal to participate or withdrawal of informed consent. Insufficient clinical, forensic, or follow-up data for longitudinal analysis.

The study population consists of adult offenders with mental disorders recruited from forensic psychiatric care systems in Italy and California. Participants are enrolled at the time of the application of a security measure or upon admission to a forensic facility, including both custodial and non-custodial settings.

In the Italian cohort, participants include individuals placed under security measures within the National Health Service, such as those admitted to REMS or managed in community-based forensic or psychiatric services. This group reflects the community-oriented Italian forensic model, characterized by rehabilitative pathways and integration with territorial mental health services.

In the California cohort, participants are recruited from high-security forensic hospitals and community forensic programs under the Department of State Hospitals, including individuals deemed incompetent to stand trial (IST) or not guilty by reason of insanity (NGRI). This population reflects a h