The thyroid gland is an important organ of the endocrine system. It is located at the front of the neck, just above where your collarbones meet. The thyroid makes hormones that control the way every cell in the body uses energy. This process is called metabolism.
Hypothyroidism is more common in women and people over age 50.
The most common cause of hypothyroidism is thyroiditis. Swelling and inflammation damage the thyroid gland's cells.
Causes of this problem include:
The immune system attacking the thyroid gland
Viral infections (common cold) or other respiratory infections
Pregnancy (often called postpartum thyroiditis)
Other causes of hypothyroidism include:
Certain medicines, such as lithium and amiodarone
Congenital (birth) defects
Radiation treatments to the neck or brain to treat different cancers
Radioactive iodine used to treat an overactive thyroid gland
Surgical removal of part or all of the thyroid gland
Sheehan syndrome, a condition that may occur in a woman who bleeds severely during pregnancy or childbirth and causes the destruction of the pituitary gland
Treatment is aimed at replacing the thyroid hormone you are lacking.
Levothyroxine is the most commonly used medicine:
You will be prescribed the lowest dose possible that relieves your symptoms and brings your blood hormone levels back to normal.
If you have heart disease or you are older, your doctor may start you on a very small dose.
Most people with an underactive thyroid will need to take this medicine for life.
When starting you on your medicine, your doctor may check your hormone levels every 2 to 3 months. After that, your thyroid hormone levels should be monitored at least once every year.
When you are taking thyroid medicine, be aware of the following:
DO NOT stop taking the medicine even when you feel better. Continue taking it exactly as your doctor prescribed.
If you change brands of thyroid medicine, let your doctor know. Your levels may need to be checked.
What you eat can change the way your body absorbs thyroid medicine. Talk with your doctor if you are eating a lot of soy products or are on a high-fiber diet.
Thyroid medicine works best on an empty stomach and when taken 1 hour before any other medicines. Ask your doctor if you should take your medicine at bedtime. Taking it at bedtime may allow your body to absorb the medicine better than taking it in the daytime.
Wait at least 4 hours after taking thyroid hormone before you take fiber supplements, calcium, iron, multivitamins, aluminum hydroxide antacids, colestipol, or medicines that bind bile acids.
While you are taking thyroid replacement therapy, tell your doctor if you have any symptoms that suggest your dose is too high, such as:
In most cases, thyroid hormone level becomes normal with proper treatment. You will likely take a thyroid hormone medicine for the rest of your life.
Myxedema coma, the most severe form of hypothyroidism, is rare. It occurs when thyroid hormone levels get very low. It can be caused by an infection, illness, exposure to cold, or certain medicines in people with untreated hypothyroidism.
Myxedema coma is a medical emergency that must be treated in the hospital. Some patients may need oxygen, breathing assistance (ventilator), fluid replacement, and intensive-care nursing.
Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract. 2012;18:988-1028. PMID: 23246686 www.ncbi.nlm.nih.gov/pubmed/23246686.
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.