Hyperthyroidism is too much thyroid hormone in the blood. The thyroid gland is in the front of the neck. It makes two hormones that control metabolism, such as:

  • How many calories you burn
  • How warm you feel
  • How much you weigh
  • How the body handles things that the heart, gastrointestinal, and nervous system do

The Thyroid Gland

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Graves disease is the most common. It causes the immune system to make antibodies that cause the thyroid gland to make too much hormone.

Hyperthyroidism can also be from:

  • Swelling of the thyroid
  • A nodule on the thyroid
  • Taking too much thyroid replacement
  • Substances made by tumors of the thyroid gland, testes, or ovaries
  • Consuming too much iodine (rare)

Treating hyperthyroidism can lead to hypothyroidism. This is when the gland does not make enough hormone.