Weight Gain Associated with Levothyroxine Treatment

Mechanisms of Weight Gain

Overtreatment with levothyroxine can lead to iatrogenic hyperthyroidism, resulting in weight gain, as reported by the American College of Physicians, with about 25% of patients on levothyroxine being unintentionally maintained on doses high enough to suppress TSH completely 1
Undertreatment with levothyroxine may not fully address the metabolic effects of hypothyroidism, potentially leading to weight gain, according to clinical guidelines 2

Regular monitoring of TSH levels every 6-8 weeks while titrating hormone replacement, and then every 6-12 months once stable, is essential to prevent both overtreatment and undertreatment, as recommended by clinical guidelines 2
Overtreatment with levothyroxine can increase the risk for osteoporosis, fractures, abnormal cardiac output, and ventricular hypertrophy, highlighting the importance of appropriate dosing, as reported in the Annals of Internal Medicine 1
Appropriate dosing is critical, with the full replacement dose being approximately 1.6 mcg/kg/day for patients under 70 years without cardiac disease, and starting with 25-50 mcg/day and titrating gradually for patients over 70 years or with cardiac disease, according to clinical guidelines 2