Substance use disorders, particularly alcohol use disorder (AUD), are a major global health challenge, significantly impacting morbidity and mortality rates. In the Netherlands, around 20% of the population is affected by excessive alcohol consumption, with a notable treatment gap and disproportionate effects on the elderly. Despite increased research into AUD treatments, patient numbers remain stable, straining healthcare systems. Moreover, the Dutch government anticipates that addressing the needs of both diagnosed and undiagnosed patients, the workforce should be increased in the general healthcare sector from the current level of 16.67% to 25% of the total Dutch workforce by 2040. Furthermore, existing regulations and policies appear inadequate in effectively managing these demands. This study aims to explore the socio-organisational drivers and policy effects on the Dutch mental health care system, focusing on AUD, to maintain sustainable quality care. It examines organizational drivers, expert perspectives, policy influence on system dynamics, and the relationship between capacity shortages and care quality. The research employs a mixed-method approach, including a literature review, exploratory interviews, a Participatory System Dynamics Modeling (PSDM) workshop, and a comparative analysis of data from 12 mental health services (MHS). Key findings include the significance of internal factors like patient satisfaction and therapeutic alliance, and the crucial role of over and undertreatment considerations during treatment processes. External factors like self-coping, and individualization and blurring of alcohol in shops also influence both treatment effectiveness and alcohol consumption. Current policy regulations inadvertently contribute to capacity shortages and treatment gaps. System Dynamics (SD) modelling reveals that increased regulatory pressures and quality care demands lead to capacity being consumed by administrative tasks and budget gaps. This relates to a 'fixes that fail' archetype, combined with social dynamics like an ageing population and increased alcohol consumption, exacerbates the 'growth and underinvestment' archetype in the Dutch mental healthcare system. The study highlights the unintended consequences of current policies, such as disjointed preventive measures and reduced practitioner autonomy. It also emphasizes the complexity of healthcare systems as revealed by the challenge of identifying cause-and-effect due to multiple aggregational levels, the diverse perspectives on the system both by literature and experts, the varied healthcare contexts and the multi-disciplinary and collaborative nature of (mental) healthcare. Key limitations include not fully addressing safety in health quality and challenges in integrating quantitative methods. This thesis underscores the importance of a holistic approach in healthcare, considering both social and organizational aspects. It suggests that current policies may lead to over-regulation or insufficient prevention awareness, impacting both society and MHS organisations. Adopting a holistic system approach can enhance further understanding of policy impacts crucial for preventing a growing treatment-capacity gap and ensuring a sustainable mental health care system for society’s vulnerable members.