Dose Optimization of Levothyroxine in Diabetic Patients Receiving Metformin or Antihypertensive Drugs: A Clinical Correlation Study in Dhaka

Background: The coexistence of diabetes mellitus (DM) and hypothyroidism (HT) presents significant clinical challenges. Both conditions influence metabolism, cardiovascular health, and pharmacological responses. Metformin, the cornerstone of DM management, and antihypertensive drugs such as beta-blockers and ACE inhibitors, may alter thyroid hormone metabolism and serum thyroid-stimulating hormone (TSH) levels, influencing the required levothyroxine dose. However, limited data exist from South Asian populations where polypharmacy and genetic metabolic variability may affect these interactions. Objective: To evaluate levothyroxine dose requirements in diabetic-hypothyroid patients receiving metformin and/or antihypertensive therapy and assess the correlation between drug regimen, TSH levels, and glycemic control. Methods: Methods: A cross-sectional comparative study involving 286 adults (160 females, 126 males; aged 25–70 years) was conducted between August 2024 and July 2025 at a tertiary care medical facility and its affiliated endocrinology clinics in Dhaka, Bangladesh. Participants were categorized into four groups: Group A: Metformin only (n = 71) Group B: Antihypertensive only (n = 72) Group C: Both Metformin and Antihypertensives (n = 70) Group D: Control (no such drugs; n = 73) Results: Patients using metformin required lower mean levothyroxine doses and exhibited lower serum TSH levels compared to other groups (p < 0.001). A significant negative correlation was observed between metformin use and TSH levels ( r = –0.63, p < 0.01 ). In contrast, antihypertensive therapy, especially beta-blockers, was associated with slightly higher TSH values ( r = +0.28, p < 0.05 ). Conclusion: Metformin use was associated with lower TSH levels and reduced levothyroxine requirements, while antihypertensives, particularly beta-blockers, modestly increased dose needs. Optimizing levothyroxine dosing based on concurrent medication profiles can improve metabolic and cardiovascular outcomes in diabetic-hypothyroid patients.