What is the main MOA of Levothyroxine (Synthroid)?

What is the main MOA of Levothyroxine (Synthroid)?

• A. Inhibits peripheral conversion of T4 to T3
• B. Suppresses TSH production
• C. Synthetic T4 hormone
• D. Blocks thyroid hormone receptors

Answer: (C)

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4) used to replace deficient thyroid hormone. Its main action is to provide T4 so the body can maintain normal thyroid hormone levels. In the body, this T4 is converted to the more active T3 in tissues, and T3 then binds to thyroid hormone receptors in cells to regulate the transcription of many genes involved in metabolism, energy use, and growth. This replacement restores normal metabolic function and, through feedback, helps reduce TSH to appropriate levels when thyroid hormone is adequate. So, the best description is that levothyroxine is a synthetic T4 hormone—provided to replace deficient thyroid hormone. It is not an inhibitor of T4 to T3 conversion, not a receptor blocker, and its suppression of TSH is a downstream effect of hormone replacement rather than its primary action.

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4) used to replace deficient thyroid hormone. Its main action is to provide T4 so the body can maintain normal thyroid hormone levels. In the body, this T4 is converted to the more active T3 in tissues, and T3 then binds to thyroid hormone receptors in cells to regulate the transcription of many genes involved in metabolism, energy use, and growth. This replacement restores normal metabolic function and, through feedback, helps reduce TSH to appropriate levels when thyroid hormone is adequate.

So, the best description is that levothyroxine is a synthetic T4 hormone—provided to replace deficient thyroid hormone. It is not an inhibitor of T4 to T3 conversion, not a receptor blocker, and its suppression of TSH is a downstream effect of hormone replacement rather than its primary action.