It is estimated that 50% of patients do not take their medications as prescribed. Medication non-adherence is a complex problem that contributes to suboptimal health outcomes, however improving non-adherence is challenging.

Medication non-adherence includes primary non-adherence (where patients do not fill or refill the initial prescription or an appropriate alternative within a clinically acceptable time period) and secondary non-adherence (the prescription is filled but the medicine is not used as prescribed).

There is limited published evidence on primary non-adherence, as most studies focus on secondary non-adherence. A study which assessed primary non-adherence among community-dwelling patients in British Columbia (BC) was recently published (CMAJ August 2023;195(30):E1000-9).

The study used linked prescribing data from primary care electronic medical records to pharmacy dispensing claims between January 2013 and April 2019 in BC. The study cohort included all individuals who visited their primary care provider and had ≥one prescription written during the study period. In this study, primary non-adherence was defined as failure to fill a new prescription or its equivalent (defined as those with the same first 7 digits of the active ingredient code) within 6 months of the prescription issue date. Multivariable logistic regression was used to assess prescriber, patient and medication factors associated with primary non-adherence among the study cohort.

The study cohort included 57 primary care providers and 34,243 patients; there were 150,565 new prescriptions written during the study period of which 25,649 were not filled within 6 months of the prescription issue date, which represented an overall prevalence of primary non-adherence of 17%. The highest prevalence of non-adherence was for dermatological medicines (27%) and the lowest among cardiovascular medicines (9.1%); adherence was higher for medicines that could be prescribed for rapid symptom relief or on an as-needed basis (e.g. topical corticosteroids [35.1%] and antihistamines [23.4%]). The study reported that 82.1% of the prescriptions were dispensed within 2 weeks. Primary non-adherence decreased with increasing age (OR 0.91, 95% CI 0.90 to 0.92 for each additional 10 years), however it significantly increased in those aged ≥65 years with polypharmacy but not for those <65 years.

A limitation of the study is that the authors cannot exclude residual confounding or selection effects that may influence the results. They conclude that the prevalence of primary non-adherence to new prescriptions was 17% in the study and that interventions to address primary non-adherence could target older patients with polypharmacy and within the first two weeks of the issue date of the prescription.

[Editor’s note: further information on medication non-adherence can be found in the NMIC bulletin 2022;Volume 28: No 24 – overview of medication non-adherence]

Where this study fits: interventions to address primary non-adherence could target older patients with polypharmacy