In England and Wales, detained psychiatric inpatients are treated under section 63 of the Mental Health Act 1983. This paper critically analyses the relevant law and considers the arbitrary distinctions between consent for treatments for mental illnesses and physical conditions, which may disempower patients with mental illness. Section 63 states that (for detained psychiatric patients) consent for medical treatment for patients’ mental disorder is not required. The treating clinician responsible for a patient decides what this medical treatment entails. This article focuses on three main legal cases: B v Croydon Health Authority, Tameside and Glossop v CH and Nottinghamshire Healthcare NHS Trust v RC and considers whether s 63 disempowers patients with mental illnesses.