What is hypothyroidism?

If there is not enough thyroid hormone in the bloodstream, your body’s metabolism slows down. This condition is called hypothyroidism (also known as underactive thyroid disease). It is a relatively common disease that affects people of all ages and races. However, women, especially older women, are more likely to develop hypothyroidism than men are. Hypothyroidism can affect up to 20% of women over the age of 50.

What is the thyroid gland?

The thyroid is a small butterfly-shaped gland located just below the Adam’s apple. The primary function of the thyroid is to control the body’s metabolism (the rate at which the cells perform duties essential to living).

To control the metabolism, the thyroid produces the hormones T4 and T3, which tell the body’s cells how much energy to use. These hormones act on almost all the tissues and organs of the body. They help control your body temperature, influence your heart rate, and regulate the production of protein.

A properly functioning thyroid will maintain the right amount of hormones needed to keep your body’s metabolism functioning at a satisfactory rate. As the hormones are used, the thyroid creates replacements. The quantity of the thyroid hormones in the bloodstream is monitored and controlled by the pituitary gland, which is located in the center of the skull below the brain. When the pituitary gland senses either a lack of thyroid hormone or too much, it will adjust its own hormone (thyroid stimulating hormone, or TSH) and send it to the thyroid to tell it what to do.

What causes hypothyroidism?

The most common cause of hypothyroidism is a disorder known as autoimmune thyroiditis (Hashimoto’s disease). The body’s immune system causes the thyroid gland to lower the amount of hormones produced. Hashimoto’s disease can be hereditary, meaning it runs in families.

Thyroiditis (inflammation of the thyroid) can also occur after pregnancy or a viral illness. Treatment with radioactive iodine for hyperthyroidism (overactive thyroid) can result in hypothyroidism. Additionally, several medicines (lithium and amiodarone) can affect thyroid function.

Another potential cause of hypothyroidism is a problem with the pituitary gland. The pituitary might fail to stimulate the thyroid to make enough hormones to meet the body’s needs.

What are the symptoms of hypothyroidism?

The symptoms of hypothyroidism usually develop slowly over a number of years and include:

  • Fatigue
  • Numbness and tingling in hands
  • Constipation
  • Weight gain
  • Intolerance to cold
  • Dry, coarse skin and hair
  • Decreased sexual interest
  • Frequent, heavy menstrual periods
  • Forgetfulness

Last reviewed by a Cleveland Clinic medical professional on 02/05/2017.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy