People with severe mental illness (SMI) are at greater risk of developing diabetes, heart disease and strokes. We aim to examine the long-term effect of antipsychotics on these physical health outcomes in people with SMI. Using electronic primary care records, we will analyse long-term changes in antipsychotic prescription patterns. Then, we will compare people’s body weight, blood pressure and cholesterol before and after the initiation of antipsychotic treatment to understand the long-term impact on physical health. Clinical findings will help patients and their doctors understand how antipsychotics can affect physical health in the long term and inform future treatment decisions.