A disorder of the immune system that causes the thyroid gland to make too much thyroid hormone — a condition called hyperthyroidism.

In Graves' disease, the body's disease-fighting immune system makes an antibody to part of the cells in the thyroid. It's not clear why this happens. The antibody is what causes the thyroid to make too much thyroid hormone. Although Graves' disease may affect anyone, it's more common among women and in people younger than 40.

Symptoms of Graves' disease can be wide ranging. They may include a slight tremor of the hands or fingers, heat sensitivity, weight loss, an enlarged thyroid gland, bulging eyes, thick, red skin on the shins or feet, menstrual cycle changes, problems getting an erection, low sex drive, and fast or irregular heartbeat, among other symptoms.

Treatment for Graves' disease may include medicine that lowers the amount of hormone the thyroid makes, medicine that blocks the effects of thyroid hormone on the body, radioactive iodine therapy to destroy overactive thyroid cells, and surgery to remove all or part of the thyroid.