Copayments for prescription medicines on a public health insurance scheme in Ireland

Purpose: We assessed the impact of the introduction of a €0.50 prescription copayment, and its increase to €1.50, on adherence to essential and less-essential medicines in a publicly insured population in Ireland. Methods: We used a pre-post longitudinal repeated measures design. We included new users of essential medicines: blood pressure lowering, lipid lowering and oral diabetic agents, thyroid hormone, anti-depressants, and less-essential medicines: non-steroidal anti-inflammatory drugs (NSAIDs), Proton Pump Inhibitors/H2 antagonists (PPIs/H2), and anxiolytics/hypnotics. The outcome was change in adherence, measured using Proportion of Days Covered. We used segmented regression with generalised estimating equations to allow for repeated measurements. Results: Sample sizes ranged from 7145 (thyroid hormone users) to 136111 (NSAID users). The €0.50 copayment was associated with reductions in adherence ranging from -2.1%[95% CI, -2.8 to -1.5] (thyroid hormone) to -8.3%[95% CI, -8.7 to -7.9] (anti-depressants) for essential medicines and reductions in adherence of -2%[95% CI, -2.3 to -1.7] (anxiolytics/hypnotics) to -9.5%[95% CI, -9.8 to -9.1] (PPIs/H2) for less-essential medicines. The €1.50 copayment generally resulted in smaller reductions in adherence to essential medicines. Anti-depressant medications were the exception with a decrease of -10.0% [95% CI, -10.4 to -9.6] after the copayment increase. Larger decreases in adherence were seen for most less-essential medicines; the largest was for PPIs/H2 at -13.5% [95% CI, -13.9 to -13.2] after the €1.50 copayment. Conclusion: Both copayments had a greater impact on adherence to less-essential medicines than essential medicines. The major exception was for anti-depressant medicines. Further research is required to explore heterogeneity across different socio-economic strata and to elicit the impact on clinical outcomes.