One-Year Evolution of Multi-Morbidity, Polypharmacy, And Medication Regimen Complexity Among Adults with Chronic Conditions Attending Outpatient Care: A Prospective Longitudinal Cohort Study

Background: Multi morbidity is increasingly common in adult outpatient practice and frequently results in the use of multiple medications and increasingly demanding treatment schedules. Although medication count is commonly used to describe polypharmacy, it does not fully capture the complexity of a patient's treatment regimen. Dosage forms, dosing frequency, and additional administration instructions may substantially influence the practical burden of medication use. Objective: To assess the one-year evolution of multi morbidity, polypharmacy, and medication regimen complexity among adults receiving longitudinal outpatient care. Methods: A prospective longitudinal cohort study was conducted among adults aged 18 years or older receiving ongoing outpatient care for chronic medical conditions. Participants were assessed at baseline, 6 months, and 12 months. Multi morbidity was defined as the presence of two or more chronic conditions. Polypharmacy was defined as the concurrent use of five or more long-term medications, while hyper-polypharmacy was defined as the use of ten or more medications. Medication regimen complexity was assessed using the Medication Regimen Complexity Index (MRCI). Results: A total of 1,250 adults were enrolled, and 1,128 (90.2%) completed the 12-month follow-up. The reported prevalence of multi morbidity increased from 54.2% at baseline to 61.8% at 12 months. Polypharmacy increased from 38.4% to 45.6%, while hyper-polypharmacy increased from 11.2% to 15.1%. Mean MRCI increased from 14.2 ± 6.1 at baseline to 18.9 ± 7.4 at 12 months. Longitudinal analysis in the original study summary showed a significant increase in MRCI over follow-up. The relationship between increasing chronic disease burden and regimen complexity was also assessed. Conclusion: Multi morbidity, polypharmacy, and medication regimen complexity increased over the one-year observation period. The findings support the use of medication regimen complexity measures alongside medication counts when assessing patients with multiple chronic conditions. Regular medication review may help identify opportunities for appropriate treatment simplification and better coordination of outpatient care.