In this episode, we review the diagnostic criteria and treatment strategy of hypothyroidism including the controversy surrounding brand versus generic levothyroxine and non-levothyroxine thyroid drugs. Key Concepts The most common cause of hypothyroidism is autoimmune thyroiditis - the body attacks the thyroid gland cells. Typically in hypothyroidism, TSH levels will be high and thyroid hormone levels (T3 and T4) will be normal or low. Levothyroxine is the drug of choice to treat hypothyroidism. Doses should start low (to avoid cardiovascular side effects) and then be titrated up based on TSH levels. All other thyroid hormone formulations (including Thyroid USP, Armour Thyroid, liothyronine, etc.) are NOT recommended for use in hypothyroidism. These are not FDA approved medications and there is no data showing these products are more effective than levothyroxine. Generic formulations of levothyroxine are as effective and safe as brand-name Synthroid®. Although several levothyroxine formulations are AB compatible and can be interchanged by a pharmacist, patients should be maintained on the same formulation whenever possible. References Dong BJ, Hauck WW, Gambertoglio JG, et al. Bioequivalence of generic and brand-name levothyroxine products in the treatment of hypothyroidism. JAMA. 1997;277(15):1205-1213. Rennie D. Thyroid storm. JAMA. 1997;277(15):1238-1243. American Thyroid Association. https://www.thyroid.org/