Are payment methods for prescription drugs associated with polypharmacy in older adults in Ireland? Evidence from the TILDA cohort study

OBJECTIVES: Polypharmacy is commonly defined as the use of five or more medications, is associated with a range of adverse outcomes and is particularly common in older adults. We sought to examine the relationship between polypharmacy and payment methods for prescription drugs among older adults in Ireland. METHODS: This is a cross-sectional analysis of data from wave 3 of The Irish Longitudinal Study on Aging, a nationally representative cohort study sample of community-living adults aged 50 years and older in Ireland. We used multivariable logistic regression to model the independent relationship between polypharmacy and drug payment methods. We controlled for a wide range of demographic, socioeconomic and health-related variables. RESULTS: Enrolment in publicly funded schemes which entitle participants to subsidised or free prescription medications was independently associated with increased odds of reporting polypharmacy. Relative to out-of-pocket payment, we found polypharmacy was independently associated with payment via medical card (OR 2.65; 95% CI 2.13 to 3.28), drugs payment scheme (OR 3.83; 95% CI 2.96 to 4.95), long-term illness scheme (OR 4.24; 95% CI 3.06 to 5.87), but not private health insurance (OR 0.82; 95% CI 0.42 to 1.62). CONCLUSIONS: Given multiple payment methods available for funding prescription charges in Ireland, there is a significant differential in the upfront costs faced by patients. One implication of our results is that the quantity of medications consumed by an individual may be influenced by payment methods for prescription fees. This could lead to overconsumption of medicines by those who are covered, or underconsumption by those who are not. However, our study was limited by an inability to discriminate between appropriate and inappropriate polypharmacy or to account for differential levels of multimorbidity, suggesting further research on this topic is warranted.