Overview
What Levothyroxine Replaces
Hypothyroidism develops when the thyroid cannot produce enough thyroxine (T4) and triiodothyronine (T3).
REx-PN
REx-PN
Hypothyroidism develops when the thyroid cannot produce enough thyroxine (T4) and triiodothyronine (T3). Low circulating thyroid hormone slows metabolic activity throughout the body. The pituitary responds by increasing thyroid-stimulating hormone (TSH), attempting to push the thyroid to produce more hormone. Levothyroxine is synthetic T4. It restores the body’s thyroid hormone supply and is converted in peripheral tissues to active T3 as needed. The goal is not simply to improve fatigue or constipation; it is to restore euthyroid physiology without causing excess thyroid hormone. The medication works slowly because T4 has a long half-life and tissue effects normalize gradually. A patient may feel somewhat better before laboratory values fully reflect a dose change. For that reason, dose adjustments are guided by scheduled TSH testing rather than day-to-day symptoms alone.
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