The disparity in health outcomes associated with mental illness or addiction is one of the starkest in New Zealand. Individuals using mental health services have twice the risk of dying before age 65 compared to other New Zealanders, mainly from chronic medical conditions. And Māori with mental illness or addiction may be doubly disadvantaged in their physical health. This project focuses on the health system as a solution to this disparity. We will use linked health datasets, online surveys and qualitative interviews to investigate unequal treatment and outcomes for physical health conditions in people with mental illness or addiction compared to other New Zealanders. We will develop health system interventions focused on providing service users and clinicians the tools and understanding to seek and provide appropriate care for physical health needs in the context of mental illness or addiction. Learning from lived experience is integral to this project.