People living with depression are at increased risk of poor health outcomes, including dementia. Interventions to reduce dementia risk (dementia risk reduction (DRR)), include physical activity, diet and vascular health interventions. These can also benefit depressive symptoms and broader health, making DRR an important part of holistic mental health care for depression. However, enabling engagement and adherence, and embedding interventions in mental health clinician practice are ongoing challenges that limit the impact of interventions and implementation in clinical practice. Improved intervention tailoring and new approaches to intervention design and implementation are urgently needed. Co-design approaches have been shown to improve engagement and the impact of complex interventions in diverse fields, but have not previously been used in DRR.

The ENGAGED study will examine DRR intervention needs specifically for people living with depression, then co-design a tailored DRR intervention for use in mental health clinical settings.

The study will adapt a co-design model for mental health settings that emphasizes lived-expertise, and incorporate processes and evidence from behavioral science. Participants will include middle-aged and older people living with depression, and mental health clinicians.

Semi-structured interviews with both participant groups will examine unmet intervention needs. Illuminated shared experiences and themes will be explored further through focus group discussions to develop consensus intervention priorities. They will also be analyzed to produce a contextualized model of relevant behavior change. Participants and researchers will then work together to co-design intervention components and refine prototypes. Finally, mixed methods survey will evaluate the co- design process and participant experiences.

This study will provide two key outputs to enhance future intervention tailoring and engagement:

1. 1. 1) a pragmatic blueprint for DRR intervention with people experiencing depression across diverse mental health clinical settings, ready for evaluation and implementation

2. 2. 2) a model of DRR behavior change that is specified to this population.

This research addresses the need for new approaches to tailored, integrated mental, physical and cognitive healthcare for people living with depression that emphasize stakeholder expertise and engagement to facilitate holistic support.