What is Hypothyroidism?

Hypothyroidism is the reduced production of thyroid hormones by the thyroid gland.


Causes and Risk Factors

Under the control of thyroid-stimulating hormone (TSH) from the pituitary, the thyroid gland produces thyroid hormones thyroxine (T4) and triiodothyronine (T3).  Thyroid hormones affect metabolism, heat production as well as growth and development.

Disorder of the thyroid, like all endocrine glands, can lead to the following:

  • Goitre – gland swelling
  • Hyperthyroidism– increased production of thyroid hormones
  • Hypothyroidism – reduced thyroid function

The most common cause of hypothyroidism is autoimmune diseases. It can also arise from thyroid removal or radioactive iodine (RAI) treatment of the thyroid. Secondary hypothyroidism can arise from pituitary disease. A blood test with low thyroid hormones and raised TSH confirms the diagnosis of primary hypothyroidism.



  • Weight gain
  • Cold intolerance
  • Tiredness
  • Poor mental function
  • Raised serum cholesterol



Treatment for hypothyroidism is almost always life-long replacement with L-thyroxine. The dose is adjusted to achieve the dose that normalises the thyroid hormone and TSH levels.


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