Hypothyroidism: MedlinePlus Medical Encyclopedia
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid.
The thyroid gland is an important organ of the
. 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
.
Hypothyroidism is more common in women and people over age 50.
The most common cause of hypothyroidism is thyroiditis. In people with thyroiditis, swelling and inflammation (usually low grade) 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, and some types of
Congenital (birth) defects
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
, a condition that may occur in a woman who bleeds severely during pregnancy or childbirth and causes the destruction of the pituitary gland (which regulates the thyroid gland)
or pituitary surgery
Early symptoms:
Hard stools or constipation
Feeling cold (wearing a sweater when others are wearing a t-shirt)
Fatigue or feeling slowed down
Heavier and irregular menstrual periods
Paleness or dry skin
Sadness or
Thin, brittle hair or
Late symptoms, if untreated:
Decreased taste and smell
Hoarseness
Puffy face, hands, and feet
Slow speech
Thickening of the skin
Thinning of eyebrows
Low body temperature
Slow heart rate
The health care provider will do a
and may find that your thyroid gland is enlarged. Sometimes, the gland is normal size or smaller-than-normal. The exam may also reveal:
High diastolic blood pressure (second number)
Thin brittle hair
Coarse features of the face
Pale or dry skin, which may be cool to the touch
Reflexes that have a delayed relaxation phase
Swelling of the arms and legs
Blood tests are also ordered to measure a thyroid hormone (free thyroxine or free
) and a pituitary hormone that regulates the thyroid gland (thyroid stimulating hormone or
).
Specialized thyroid tests like thyroid peroxidase antibodies may be needed.
You may also have tests to check:
Complete blood count (
)
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 thyroid hormone levels back to normal.
If you have heart disease or you are older, your provider may start you on a very small dose.
Most people with an underactive thyroid will need to take this medicine for life.
Levothyroxine is usually a pill, but some people with very severe hypothyroidism first need to be treated in the hospital with intravenous levothyroxine (given through a vein).
When starting you on this medicine, your provider 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 provider prescribed.
If you change brands of thyroid medicine, let your provider know. Your levels may need to be checked.
What you eat can change the way your body absorbs thyroid medicine. Talk with your provider 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 provider 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 provider if you have any symptoms that suggest your dose is too high, such as:
Anxiety
Rapid weight loss
Restlessness or shakiness (tremors)
Sweating
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 crisis (also called myxedema coma), the most severe form of hypothyroidism, is rare. It occurs when thyroid hormone levels get very, very low. The severe hypothyroid crisis is often then started by an infection, illness, exposure to cold, or certain medicines (opioids are a common cause) in people with severe hypothyroidism. It can also commonly be caused by failure to take prescribed thyroid hormone consistently or correctly.
Myxedema crisis is a medical emergency that must be treated in the hospital. Some people may need oxygen, breathing assistance (ventilator), fluid replacement, and intensive-care nursing.
Symptoms and signs of myxedema coma include:
Below normal body temperature
Decreased breathing
Unresponsiveness
Inappropriate or uncharacteristic moods
People with untreated hypothyroidism are at increased risk of:
Infection
,
, giving birth to a baby with birth defects
because of higher levels of LDL (bad) cholesterol
Heart failure
Contact your provider if you have symptoms of hypothyroidism.
If you are being treated for hypothyroidism, contact your provider if:
You develop
or rapid heartbeat
Your symptoms get worse or do not improve with treatment
You develop new symptoms
Myxedema; Adult hypothyroidism; Underactive thyroid; Goiter - hypothyroidism; Thyroiditis - hypothyroidism; Thyroid hormone - hypothyroidism
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Updated by: Sandeep K. Dhaliwal, MD, board-certified in Diabetes, Endocrinology, and Metabolism, Springfield, VA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.