Background A diagnosis of serious mental illness can impact on the whole family. Families informally provide significant amounts of care but are disproportionately at risk of carer burden when compared to those supporting people with other long-term conditions. Shared decision making (SDM) is an ethical model of health communication associated with positive health outcomes; however, there has been little research to evaluate how routinely family is invited to participate in SDM, or what this looks like in practice. Objective This UK study aimed to better understand how the family caregivers of those diagnosed with SMI are currently involved in decision making, particularly decisions about treatment options including prescribed medication. Objectives were to Explore the extent to which family members wish to be involved in decisions about prescribed medication, Determine how and when professionals engage family in these decisions, Identify barriers and facilitators associated with the engagement of family in decisions about treatment., Participants Open-ended questions were sent to professionals and family members to elicit written responses. Qualitative responses were analysed thematically. Results Themes included the definition of involvement and 'rules of engagement.' Staff members are gatekeepers for family involvement, and the process is not democratic. Family and staff ascribe practical, rather than recovery-oriented roles to family, with pre-occupation around notions of adherence. Conclusions Staff members need support, training and education to apply SDM. Time to exchange information is vital but practically difficult. Negotiated teams, comprising of staff, service users, family, peers as applicable, with ascribed roles and responsibilities could support SDM.