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. Copyright © 2015 John Wiley & Sons, Ltd.