[Clinical determinants of levothyroxine dosage adjusted for various body weights]

Hypothyroidism requires treatment with levothyroxine to achieve a euthyroid state. Dosage based solely on body weight has limitations, particularly in patients with overweight or obesity.

To evaluate whether the levothyroxine dose required to achieve a euthyroid state, adjusted for different body weight measures, varies according to sex, age, body mass index (BMI), and type of hypothyroidism.

An analytical cross-sectional study was conducted in euthyroid adults with hypothyroidism receiving levothyroxine therapy between August 2024 and August 2025. Patients with recent dose adjustments or conditions affecting drug absorption were excluded. Absolute doses and doses adjusted for actual body weight, ideal body weight, adjusted body weight, and fat-free mass were analyzed.

A total of 101 patients were included; 76.2% were women and 23.8% men, with a mean age of 50.8 ± 14.9 years. Women received higher levothyroxine doses adjusted for ideal body weight and fat free mass than men. Overweight and obese patients received higher total doses and higher ideal weight adjusted doses than patients with normal BMI. No differences were observed in levothyroxine dose adjusted for any body weight for age or type of hypothyroidism.

Sex influences levothyroxine doses adjusted for ideal body weight and fat free mass, while BMI status influences total and ideal weight adjusted doses.