Which medication is commonly used to inhibit thyroid hormone synthesis?

Methimazole is commonly used to inhibit thyroid hormone synthesis, making it an effective medication for managing conditions such as hyperthyroidism. It achieves this by blocking the action of the thyroid peroxidase enzyme, which is crucial in the production of thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). By reducing the synthesis of these hormones, Methimazole helps to regulate excessive thyroid function and alleviate symptoms associated with hyperthyroidism, such as increased heart rate, weight loss, and anxiety.

In contrast, other medications listed serve different purposes. Propranolol is primarily a beta-blocker used to manage symptoms of increased heart rate and anxiety but does not directly inhibit thyroid hormone synthesis. L-thyroxine is a synthetic form of the thyroid hormone and is used primarily to treat hypothyroidism, which is the opposite of conditions treated by Methimazole. Calcium carbonate, on the other hand, is a supplement used to treat or prevent calcium deficiency and has no role in thyroid hormone synthesis. Hence, Methimazole is the appropriate choice for inhibiting the synthesis of thyroid hormones.