In hyperthyroidism, your thyroid gland is overactive. It produces too much thyroid hormone. This can cause many of your body’s functions to speed up.

Hyperthyroidism affects between 1 and 3 percent of people in the United States and is more common in women.

Graves’ disease is the most common cause of hyperthyroidism, affecting about 70 percent of people with an overactive thyroid. Nodules on your thyroid — a condition called toxic nodular goiter or multinodular goiter — can also cause the gland to overproduce its hormones.

Hyperthyroidism can also be caused by:

• thyroid gland inflammation
• too much iodine intake
• taking too much thyroid hormone medication
• overactive thyroid nodules, also known as toxic nodular goiter or multinodular goiter
• noncancerous pituitary gland tumor

Hyperthyroidism symptoms

Excessive thyroid hormone production may lead to symptoms that can include:

• restlessness
• nervousness
• racing heart rate
• irritability
• increased sweating
• shaking
• anxiety
• trouble sleeping
• thin skin
• brittle hair and nails
• muscle weakness
• weight loss
• increased appetite
• frequent bowel movements
• bulging eyes (in Graves’ disease)