The impact of a co-payment increase on the consumption of type 2 antidiabetics - A nationwide interrupted time series analysis.

International literature suggests that co-payment increases are associated with decreased medicine use, although the effects depend on context. We examined the impact of a co-payment increase on the consumption of type 2 antidiabetics in Finland, a country with a comprehensive health and social security system including ceiling mechanisms aiming to protect patients from high co-payment expenditures. We used administrative register data on all reimbursed purchases of antidiabetics during 2014-2018. An interrupted time series design with segmented regression was used to examine the mean monthly purchase per person, measured as Defined Daily Doses (DDDs), before and after the co-payment increase. At baseline, the mean monthly purchase per person of type 2 antidiabetics was 105 DDDs (95% CI 103.8; 106.0;p<0.001) and there was a decreasing trend of 0.2 DDDs per month (95% CI -0.23;-0.13;p<0.001). A statistically significant decrease of 5.6 DDDs (95% CI -7.3;-3.8;p<0.001) was detected after the reform; however, no significant change in the trend was observed. No significant increase was detected in the mean monthly per person purchase of insulins. The results suggest that a co-payment increase decreases consumption of necessary medicines despite the presence of a medicine co-payment ceiling mechanism. Whether the decrease was associated with negative health effects remains to be further investigated.