What causes hypothyroidism?

Dr. Jeanne Morrison, PhD
Family Practitioner

There are a variety of causes for hypothyroidism. These include:

  • Hashimoto's disease (an autoimmune disorder)
  • Thyroiditis (an inflamed thyroid gland)
  • Congenital hypothyroidism (a birth defect)
  • Thyroidectomy (surgery that removes all or part of the thyroid gland)
  • Radiation treatments that damage or destroy the thyroid
  • Radioactive iodine (used to treat hyperthyroidism but leads to hypothyroidism after the thyroid is damaged or destroyed)
  • Viral thyroiditis (can lead to hyperthyroidism and is frequently followed by hypothyroidism)
  • Use of some drugs, especially those that treat hyperthyroidism, which then leads to hypothyroidism
  • Sheehan syndrome (sometimes occurs in women with severe bleeding while pregnant or during childbirth)
  • Iodine deficiency (very rare)

There are many different causes of an underactive thyroid (hypothyroidism). These include problems with the gland itself, such as: 

  • autoimmune processes
  • medications such as lithium and amiodarone
  • connective tissue disease such as hemochromatosis
  • postpartum inflammation of the thyroid
  • surgical removal of all or part of the thyroid
  • treatment with radioactive iodine for hyperthyroidism
  • congenital absence of the thyroid gland

Other causes of hypothyroidism include problems with the generation of the hormone from the brain that signals the thyroid gland.

Primary hypothyroidism is caused by an underlying disease of the thyroid.

The most common causes of primary hypothyroidism are autoimmune thyroiditis (i.e. Hashimoto's thyroiditis or lymphocytic thyroiditis), surgical removal of the thyroid (i.e. thyroidectomy), radioactive iodine treatment, or certain medications such as Lithium, Amiodarone.

Secondary hypothyroidism is a much less common problem. It is caused by diseases that affect the pituitary gland's ability to make and release TSH(which regulates thyroid hormone production). Specific problems include pituitary tumors, postpartum pituitary necrosis (Sheehan's syndrome—an uncommon problem where all or part of the pituitary dies after childbirth), trauma, or tumors that grow into the pituitary gland.

For more information go the
Diseases of thyroid function: Hypothyroidism

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.