Graves' disease is the most common cause of hyperthyroidism, an autoimmune disorder where antibodies stimulate the thyroid gland to overproduce hormones.

Other major causes include:

• Toxic multinodular goiter, where multiple nodules in the thyroid become overactive, often in older adults.

• Toxic adenoma (Plummer disease), a single overactive nodule in the thyroid.

• Thyroiditis, inflammation of the thyroid that causes stored hormones to leak into the bloodstream. This includes:

  • Postpartum thyroiditis (after childbirth),

  • Silent (painless) thyroiditis,

  • Subacute (de Quervain) thyroiditis (often following a viral infection).

• Excessive iodine intake, from sources like certain medications (e.g., amiodarone), cough syrups, or seaweed supplements.

• Overuse of thyroid hormone medication in patients treated for hypothyroidism.

• TSH-secreting pituitary adenomas (rare), where a tumor in the pituitary gland produces excess thyroid-stimulating hormone.

• Ectopic thyroid tissue in tumors such as struma ovarii or certain trophoblastic tumors that produce human chorionic gonadotropin (hCG), which can stimulate the thyroid.

These conditions lead to an overproduction of thyroid hormones (T3 and T4), resulting in a hypermetabolic state with symptoms such as weight loss, rapid heartbeat, anxiety, tremors, and heat intolerance.