Hypothyroidism is when the thyroid gland does not make enough hormones. The thyroid is a butterfly-shaped gland in the front of the neck. A healthy thyroid makes the hormones thyroxine (T4) and triiodothyronine (T3). These play many roles in the body, such as:
- How many calories a person burns and how much they weigh
- The speed at which the heart beats
- The temperature of a person's body
- How quickly the body breaks down food
If it is not treated, it can lead to many health problems, such as obesity and heart disease.
Hashimoto thyroiditis is the most common cause. A problem with the immune system causes it to attack thyroid gland cells.
Other causes are:
- Subacute thyroiditis
—Inflammation of the thyroid gland after a viral upper respiratory tract infection
- Medicines
—Such as those used to treat hyperthyroidism, lithium for mental health problems, and some heart medicines
- Medical treatments
—Medicines, radiation therapy, or surgery to remove part of the thyroid gland
- Idiopathic thyroid atrophy
—The thyroid tissue shrivels up for reasons that are not known
- Iodine deficiency
—The thyroid gland does not get enough iodine to make hormones (rare in the United States)
- Iodine excess
—Foods (such as shellfish) and some medicines (such as cough medicine) that have large amounts of iodine can stop the thyroid from making hormones (rare)
- Certain illnesses
—Cancers and certain infections
- Pituitary adenoma
—A non-cancerous tumor of the pituitary gland causes a problem signaling the thyroid to make hormones
- Postpartum thyroiditis
—The thyroid becomes inflamed after giving birth and does not work as it should
- Congenital hypothyroidism
—When a baby is born with problems making normal amounts of thyroid hormones
Last reviewed December 2020 by EBSCO Medical Review Board
James P. Cornell, MD
Last Updated: 2/10/2021
