What medical condition results from an overactive thyroid gland?

The medical condition that results from an overactive thyroid gland is hyperthyroidism. It occurs when the thyroid produces excessive amounts of thyroid hormones, mainly triiodothyronine (T3) and thyroxine (T4).

Because thyroid hormones accelerate many cellular processes, hyperthyroidism can cause weight loss despite increased appetite, heat intolerance, sweating, tremor, irritability, muscle weakness, frequent bowel movements, and a fast or irregular heartbeat. Blood tests typically show a low thyroid-stimulating hormone (TSH) level alongside elevated T3 or T4 levels.

The most common cause is Graves’ disease, an autoimmune condition in which antibodies stimulate the thyroid’s TSH receptors. Other causes include toxic thyroid nodules, inflammation of the thyroid, excessive iodine, or taking too much thyroid hormone medication. Graves’ disease is therefore a cause of hyperthyroidism, not the general name for the overactive-thyroid condition itself.

Hypothyroidism is the opposite disorder: the thyroid does not produce enough hormone. Treatment for hyperthyroidism depends on its cause and may include antithyroid medicines, radioactive iodine, beta blockers for symptoms, or thyroid surgery.