Capacity to give informed consent in patients with severe mental disorder in different treatment settings.

Introduction: Individuals with mental disorders, especially those in coercive or forensic settings, face unique vulnerabilities that complicate the process of obtaining informed consent. These challenges stem from both intrinsic factors (such as cognitive impairment due to psychiatric illness) and extrinsic factors (such as institutionalization or legal detention), resulting in what is often referred to as "dual vulnerability". This study implemented the German version of the Hopkins Competency Assessment Test (HCAT) and examined differences in informed consent capacity among individuals with severe mental disorders in different treatment setting, aiming to explore how institutional context affects patients' comprehension and decision-making. Methods: This study was conducted at the Psychiatric University Hospital Zurich between 2022 and 2023. Using the Hopkins Competency Assessment Test (HCAT), we assessed decision-making capacity in patients with severe mental illnesses, including schizophrenia spectrum and affective disorders, with and without comorbid substance use. Three groups were compared: forensic psychiatric inpatients, non-forensic psychiatric inpatients, and healthy controls. Results: The study involved 142 participants, mostly male, with a mean age of 37.5 years. Among clinical participants, schizophrenia spectrum disorders predominated, followed by affective disorders, and over a third had comorbid substance use disorders. Forensic psychiatric patients required more time and simpler language to complete the HCAT. They made more errors, showed increased reading effort, and achieved significantly lower comprehension scores compared to the other groups. These differences were not only explained by diagnosis, demographics, or clinical severity. Discussion: Patients with severe psychiatric disorders, especially in forensic settings, encounter unique challenges in understanding and providing informed consent. These challenges stem from both individual cognitive or clinical impairments and the institutional context, such as coercive environments and complex legal-ethical frameworks. Our findings highlight the need for setting-sensitive communication strategies, legal safeguards, and increased awareness of advance care planning in forensic institutions. Future research should not only assess capacity, but also explore patients' willingness and opportunity to participate meaningfully in ethical and legal decisions about their care. The study was registered at ClinicalTrials.gov (NCT05939765).