Background: Older adults in Ireland are at increased risk of adverse drug events (ADE) due, in part, to increasing rates of polypharmacy. Interventions to reduce ADE in community dwelling older adults (CDOA) have had limited success, therefore, new approaches are required. A realist review uses a different lens to examine why and how interventions were supposed to work rather than if, they worked. A rapid realist review (RRR) is a more focused and accelerated version. The aim of this RRR is to identify and examine the contexts and mechanisms that play a role in the outcomes relevant to reducing ADE in CDOA in the GP setting that could inform the development of interventions in Ireland. Methods: Six candidate theories (CT) were developed, based on knowledge of the field and recent literature, in relation to how interventions are expected to work. These formed the search strategy. Eighty full texts from 633 abstracts were reviewed, of which 27 were included. Snowballing added a further five articles, relevant policy documents increased the total number to 45. Data were extracted relevant to the theories under iteratively developed sub-themes using NVivo software. Results: Of the six theories, three theories, relating to GP engagement in interventions, relevance of health policy documents for older adults, and shared decision-making, provided data to guide future interventions to reduce ADEs for CDOA in an Irish setting. There was insufficient data for two theories, a third was rejected as existing barriers in the Irish setting made it impractical to use. Conclusions: To improve the success of Irish GP based interventions to reduce ADEs for CDOA, interventions must be relevant and easily applied in practice, supported by national policy and be adequately resourced. Future research is required to test our theories within a newly developed intervention.