There are numerous threats to medication safety at care transitions, which are heightened for older people, because they live with multiple long-term conditions as well as polypharmacy, and have frequent hospital admissions. Whilst evidence of the severity and scale of these medicines-related problems exists, there is insufficient detail about the lived experience of post-discharge medicines management, in particular what helps or what hinders, and how better support could be enabled. This thesis, underpinned by the Medicines Research Council framework for complex intervention design, aimed to find acceptable intervention components, which would enhance patient experience. This research followed a sequential, mixed method design to: establish the evidence base through critical literature review, develop theory using an interview study grounded in behaviour change theory, and finally to model potential intervention components by expert consensus. Interviews revealed that there were gaps in current service provision, which impacted on participants’ knowledge of and capabilities with their medicines. Despite these challenges, some participants took actions to safeguard from problems after discharge. The literature review found that effective components of trialled interventions were self-management advice, post-discharge telephone follow up and medicines reconciliation. Further behaviour change techniques from the literature, alongside expert consensus and theory-driven analysis of interview findings resulted in final selection of eight potential components. Real-world implementation of these must be coupled with key changes to current healthcare practices and policy, including better engagement with patients and carers, as well as pro-active post-discharge follow-up. Future work must carefully explore how these components can be tested pragmatically.