Key takeaways
Methimazole and Synthroid (levothyroxine) are both used to manage thyroid conditions, but they work in opposite ways. Methimazole is an antithyroid agent that treats hyperthyroidism by blocking the thyroid gland from making too much thyroid hormone. In contrast, Synthroid is a synthetic form of the T4 thyroid hormone used to treat hypothyroidism by supplementing low hormone levels. Methimazole is taken multiple times a day initially, then once daily for maintenance, while Synthroid is taken once daily on an empty stomach. Methimazole can cause side effects like rash, nausea, and vomiting, and it’s not recommended during the first trimester of pregnancy. Synthroid’s side effects are usually related to having too much thyroid hormone, such as headache and nervousness. Methimazole is only available as a generic, whereas Synthroid has both brand and generic forms available.
