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 136 111 (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.