ORIGINAL RESEARCH article
Front. Pharmacol.
Sec. Drugs Outcomes Research and Policies
Beyond prescriptions: chronic medication adherence predicts mortality risk in a large-scale cohort study
Provisionally accepted
Jessica Hamuy Blanco1*
Dina Christina Janse Van Rensburg1
Audrey Jansen Van Rensburg1
Corrie Uys2
Natalie Schellack1- 1University of Pretoria, Pretoria, South Africa
- 2Cape Peninsula University of Technology, Cape Town, South Africa
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Objectives: The Medication Adherence Risk Score (MARS) is a calculated score using pharmacy transactional data spanning 50% of the South African private pharmacy market. This study aims to demonstrate that the existing MARS model enhances risk stratification by identifying individuals at increased risk of mortality related to non-adherence to chronic medication. Methods: This was a retrospective cohort study in which an analysis of the relative mortality experience was compared to a standard fully underwritten base was performed for each of the MARS categories (low, medium, high and very high). The actual-to-expected ratio (AER) and relative risk (RR) for each category were compared across age groups and gender. The least absolute shrinkage and selection operator (LASSO) regression analysis method was applied to determine the most important variables within the dataset, providing insight into whether MARS offered more benefit than traditional risk rating factors. A time-to-event analysis by MARS categories was performed using the Cox proportional hazards model. Results: The mortality experience of the study population was higher than the expected fully underwritten base (AER = 175%). For the overall sample, increasing AER and RR did not correlate with increasing MARS categories. However, use of the MARS in addition to age band allowed for differentiation of risk within the 25 to 55 age bands, with a higher MARS score indicating a higher AER and RR. The time-to-event analysis showed a statistically significant difference in the mean number of months before death occurred between the different MARS categories (low = 26.53; medium = 8.93; high = 7.02; very high = 6.92; p < 0.001). Conclusion: The MARS is not generalisable across all groups, as evidenced by the absence of a monotonic trend in the overall sample. However, when combined with age, it effectively differentiated mortality risk for individuals aged 25-55. The standard fully underwritten model underestimated the number of deaths within this pharmacy population. The time-to-event analysis showed a significant inverse relationship between MARS category and survival time.
Keywords: Medication Adherence, Medication compliance, medication persistence, drugpersistence, Chronic medication, Mortality, death, Survival Rate
Received: 08 Sep 2025; Accepted: 14 Nov 2025.
Copyright: © 2025 Hamuy Blanco, Janse Van Rensburg, Jansen Van Rensburg, Uys and Schellack. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Jessica Hamuy Blanco, drjess.hamuyblanco@dischem.co.za
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.