BACKGROUND: Primary non-adherence refers to the patient not redeeming a prescribed medication at some point during drug therapy. Research has mainly focused on secondary non-adherence. Prior to this study, the overall rate of primary non-adherence in general practice in Iceland was not known.

OBJECTIVES: To determine the prevalence of primary non-adherence, test whether it is influenced by a moderate increase in patient copayment implemented in 2010 and examine the difference between copayment groups (general versus concession patients).

METHODS: A population-based data linkage study, wherein prescriptions issued electronically by 140 physicians at 16 primary health care centres in the Reykjavik capital area during two periods before and after increases in copayment were matched with those dispensed in pharmacies, the difference constituting primary non-adherence (population: 200 000; patients: 21 571; prescriptions: 22 991). Eight drug classes were selected to reflect symptom relief and degree of copayment. Two-tailed chi-square test and odds ratios for non-adherence by patient copayment groups were calculated.

RESULTS: The rate of primary non-adherence was 6.2%. It was lower after the increased copayment, reaching statistical significance for hypertensive agents, non-steroidal anti-inflammatory drugs (NSAIDs) and antipsychotics. Generally, primary non-adherence, except for antibacterials and NSAIDs, was highest in old-age pensioners.

CONCLUSIONS: Primary non-adherence in Icelandic general practice was within the range of prior studies undertaken in other countries and was not adversely affected by the moderate increase in patient copayment. Older patients showed a different pattern of primary non-adherence. This may possibly be explained by higher prevalence of medicine use.