左甲状腺素, also known as L-thyroxine, is a synthetic form of the thyroid hormone thyroxine (T4). It is commonly prescribed to treat conditions like hypothyroidism, where the thyroid gland does not produce enough hormones. By supplementing the body's hormone levels, 左甲状腺素 helps regulate metabolism, energy levels, and overall bodily functions. This medication is typically taken orally and is available in various dosages. Patients using 左甲状腺素 may need regular blood tests to monitor their thyroid hormone levels and adjust the dosage as necessary. It is important to follow a healthcare provider's instructions when using this medication to ensure effective treatment.