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Written by Ada’s Medical Knowledge Team

Updated on

What is hypothyroidism?

Hypothyroidism refers to a condition in which the thyroid gland produces less hormone than normal. These hormones regulate the body's metabolism (turning food into energy and controlling the speed of cell growth). The condition can be congenital (present from birth), or occur later in life as a result of thyroid damage or conditions which cause inflammation or infection in the thyroid gland. See this resource for more information on congenital hypothyroidism.

Symptoms depend on the age of the person, but include tiredness, dry hair and skin, slowed thinking and weight gain. The treatment of this condition is replacement of the thyroid hormone with medication.


The thyroid gland sits at the front of the throat, and produces a hormone (thyroid hormone) which controls metabolism (cell activity and growth). There are many causes for decreased thyroid gland function (hypothyroidism). These include not enough iodine in the diet, surgical or radiation damage to the thyroid gland, and infections or inflammation of the thyroid gland. Some children are born with a thyroid gland which does not work well. Hypothyroidism most commonly affects adults, though it can occur at any age. Both men and women are affected by the condition although it is more common in women. Some conditions that cause hypothyroidism tend to run in families, so people with a family member with hypothyroidism are often more likely to develop hypothyroidism.


The early symptoms of poor thyroid function include tiredness, constipation, brittle nails, dry hair and feeling cold. As the hypothyroidism continues, people develop a low mood, decreased motivation, slowed thinking, weight gain, a slow heart rate and a hoarse voice. Some people may develop a lump in their thyroid gland or swelling of the neck. Babies with congenital hypothyroidism (hypothyroidism since birth) have feeding difficulties, prolonged newborn jaundice (yellow skin after birth), severe constipation, and tend to move less than other babies. These babies tend to not grow and develop at the same rate as other children. Hypothyroidism in older people can be confused with dementia.


Diagnosis is based on the symptoms and clinical examination, and is confirmed by blood tests which measure the amount of hormone the thyroid gland is producing.


Treatment consists of replacing thyroid hormone with medication. Replacing thyroid hormone may require regular blood tests until the correct dosage is reached.


Avoiding radiation to the thyroid, and taking plenty of iodine in the diet can help to prevent some cases of hypothyroidism. In many countries, pregnant women and newborns are screened (tested without symptoms) for hypothyroidism. This allows early treatment and helps to prevent the consequences of undiagnosed hypothyroidism before birth and in childhood.

Other names for hypothyroidism

  • Underactive thyroid
  • Central hypothyroidism
  • Primary hypothyroidism

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