This page explains what happens if Levothyroxine and Metformin are taken together, according to official sources.
TSH reduction in patients on levothyroxine replacement
Clinical studies (Cappelli 2009, Vigersky 2006) show that metformin significantly lowers serum TSH levels in hypothyroid patients on levothyroxine without changing free T4 or causing hyperthyroidism. Patients and doctors should be aware of this effect when interpreting thyroid blood tests; do not alter dosages without consulting your physician.
Continue both medications as prescribed. Inform your physician that you are taking metformin when having thyroid panel (TSH) tests checked.
Last updated: Sep 25, 2026
Before changing or stopping any medicine, ask your doctor or pharmacist. Never stop your medicine on your own.