There is growing interest in service design to support transformation in mental healthcare. Early research in this area has shown some promising results, but has also revealed the contentious nature of this work. A better understanding of the complexity of design in mental health is needed to support the development of approaches that are appropriate for this context. As such, the aim of this paper is to examine areas of contention and related strategies employed when designing for mental health transformation. To realize this aim, a qualitative multiple case study of ten service design initiatives in mental health contexts was conducted. The analysis revealed five interconnected contentious issues: organizational constraints; ensuring meaningful participation; culture clashes; power dynamics; and systems approaches. These contentious issues are detailed and related strategies from various cases are put forward, providing a rich foundation for the ongoing development of service design approaches in mental health.