Background: Adverse drug reactions (ADRs) and adverse drug events (ADEs) are consistently reported to cause up to 30% of hospital admissions in older adults, resulting in significant morbidity, mortality and an added health economic burden.This systematic review aimed to establish the frequency of ADRs and ADEs as a cause of hospitalisation in older adults.

Methods: Standard databases and citations were searched from 2015 to 2025. Studies specifically assessing ADR and ADE prevalence and risk factors in older adults were included. The review was registered in PROSPERO (CRD42024613426) and quality was assessed using the Joanna Briggs Institute criteria with bias determined via ROBINS-E.

Results: Nine studies underwent full evaluation. The reported prevalence of ADRs ranged from 3.3% to 23.1% and ADEs ranged from 11.75% to 18% as causes of hospitalisation. The median age of those included, in the respective studies, was between 77 and 86 years. Falls (19.4%-20.9%), delirium (7.3%-12.9%) and bleeding (8%-30.2%) were the most frequently encountered ADR/ADEs causing hospitalisation. Anti-thrombotics (11.5%-30.2%) diuretics (14.7%-30.2%) and renin-angiotensin-aldosterone system (RAAS) inhibitors (7.5%-8.9%) accounted for the highest proportion of ADR/ADE causative agents.

Conclusion: This review has limitations stemming from the heterogeneity of the included studies and the exclusion of the grey literature. However, ADRs and ADEs remain a significant cause of hospital admissions in older patients. The possible preventability of these and their possible hospital admission avoidance highlights the critical need for further research into ADR/ADE risk prediction methods in addition to co-morbidity and medication optimisation for older adults.