Impact of Polypharmacy on Medication Adherence in Patients with Comorbid Type 2 Diabetes and Hypertension in Tanzania: A Cross-Sectional Study

Abstract

Abstract Background Diabetes mellitus and hypertension are increasingly prevalent non-communicable diseases that often coexist due to their interrelated pathophysiology and commonalities of risk factors. Effective management of these two comorbid conditions often involves polypharmacy, defined as the concurrent use of five or more medications, which places a substantial pill burden on patients and demands consistent medication adherence for effective disease control. In Tanzania, where access to chronic care services remains constrained and out-of-pocket medication costs can be substantial, understanding the drivers of non-adherence is considered imperative.. Limited data exist on the extent of polypharmacy and its impact on adherence among Tanzanian patients with these comorbidities. This study therefore aimed at evaluating the prevalence of polypharmacy and its impact on medication medication adherence among this population. Methodology A cross-sectional study involving 396 outpatients was conducted at Muhimbili National Hospital. Consecutive sampling was used to recruit eligible participants. Data were collected using a structured questionnaire that captured information on socio-demographics, clinical characteristics, and adherence behaviors. Polypharmacy was defined as the concurrent use of five or more medications. Medication adherence was assessed using the Medication Adherence Report Scale (MARS-5). Modified Poisson regression with robust standard errors was performed to identify factors associated with medication adherence and to estimate crude and adjusted prevalence ratios (cPR and aPR) with 95% confidence intervals. Results 71% of the study participants were on five or more medications, indicating high polypharmacy prevalence, with a median of six medications. Medication adherence was reported at 55.1%. Among participants with lower adherence, a higher proportion had elevated fasting glucose for moderate (APR: 0.83, P = 0.001) and high fasting glucose (APR: 0.66, P < 0.001), and uncontrolled blood pressure while herbal medicine use (APR: 0.72, P < 0.001) was identified as contributing factor to lower adherence.. Conclusion This study reveals a high prevalence of polypharmacy with moderate medication adherence among patients with comorbid T2DM and hypertension. These findings underscore the need for targeted interventions such as structured patient education, pharmacist-led medication reviews, and polypharmacy rationalization to improve medication adherence and clinical outcomes in this population.