Adverse Drug Reaction-Related Hospital Admissions and Adverse Drug Events and Their Association with Short- and Long-Term Health Outcomes in Older Adults

<b>Background</b>: This study examined whether adverse drug reaction (ADR)-related hospital admissions or adverse drug events (ADE) in primary care are associated with changes in health-related quality of life (HRQOL), functional decline, and A&E visits, over time, in two separate prospective cohort studies of older adults in Ireland. <b>Methods</b>: The Adverse Drug reactions in an Ageing PopulaTion (ADAPT) (Study 1: N = 230) and the Centre for Primary Care Research (CPCR) (Study 2: N = 605) prospective cohorts were used. Participants completed health outcome questionnaires at baseline and again at 3 months (Study 1) and at 24 months (Study 2). ADR-related admissions and ADEs were assessed at baseline. Multivariable linear, logistic, and ordinal logistic regressions were used to examine associations between ADR-related admissions/ADEs and changes in HRQOL (EQ-5D-5L/3L), functional decline, and A&E visits, adjusting for age, sex, comorbidity, and polypharmacy. <b>Results</b>: In Study 1 (ADAPT cohort), frailty increased and A&E visits decreased over 3 months in both ADR/non-ADR groups (<i>p</i> < 0.01). In Study 2 (CPCR cohort), HRQOL decreased, and functional decline and A&E visits increased for both ADE/non-ADE groups over 24 months (<i>p</i> < 0.05). Individuals with ADEs had lower HRQOL and greater functional decline at both time points (<i>p</i> < 0.001). However, experiencing an ADR or an ADE was not significantly associated with changes in HRQOL, functional decline, or A&E visits over time, after adjustments. <b>Conclusions</b>: There were no substantial differences in the short-term healthcare burden of ADRs, while ADEs had poorer long-term outcomes.