Medical assistance in dying for mental illness: a complex intervention requiring a correspondingly complex evaluation approach.

Medical assistance in dying for mental illness as a sole underlying medical condition (MAiD MI-SUMC) is a controversial and complex policy in terms of psychosocial and ethical medical practice implications. We discuss the status of MAiD MI-SUMC in Canada and argue for the use of the UK Medical Research Council's framework on complex interventions in programme evaluations of MAiD MI-SUMC. It is imperative to carefully and rigorously evaluate the implementation of MAiD MI-SUMC to ensure an understanding of the multiple facets of implementation in contexts permeated by unique social, economic, cultural and historical influences, with a correspondingly diverse array of outcomes. This requires a complexity-informed programme evaluation focused on context-dependent mechanisms and stakeholder experiences, including patients, service providers and other people affected by the policy. It is also important to consider the economic impact on health and social welfare systems. Such evaluations can provide the data needed to guide evidence-informed decision-making that can contribute to safer implementation and refinement of MAiD MI-SUMC.