Underactive thyroid
An underactive thyroid (hypothyroidism) occurs when the thyroid gland does not produce enough thyroid hormones. The thyroid gland, located in the neck, produces hormones that regulate metabolism, energy levels and many other bodily functions.
Hypothyroidism is common, affecting around 2% of the UK population, and is more prevalent in women and older adults. The most common cause is Hashimoto's thyroiditis, an autoimmune condition in which the immune system attacks the thyroid gland.
Symptoms develop gradually and may include:
- Tiredness, weight gain and feeling cold
- Dry skin and hair
- Constipation and muscle aches
- Low mood and difficulty concentrating
Thyroid-stimulating hormone (TSH) is the primary screening test. Elevated TSH with low free thyroxine (FT4) confirms the diagnosis. Thyroid peroxidase (TPO) and thyroglobulin antibodies help identify an autoimmune cause.
Causes of Underactive thyroid
The most common cause of hypothyroidism in the UK is Hashimoto's thyroiditis, an autoimmune condition in which the body's immune system produces antibodies that gradually destroy thyroid tissue.
Other causes include:
- Treatment for thyroid conditions, including radioactive iodine therapy or surgery for an overactive thyroid or thyroid cancer, which can result in permanently reduced thyroid function
- Medications such as lithium (used to treat bipolar disorder) and amiodarone (used for heart rhythm problems)
- Iodine deficiency, which is rare in the UK but remains a common cause worldwide
- Congenital hypothyroidism, present from birth, which is screened for in all UK newborns through the heel prick test
- Pituitary gland disorders that reduce production of thyroid-stimulating hormone (secondary hypothyroidism)
Women are five to ten times more likely to develop hypothyroidism than men. Risk increases with age and with a personal or family history of autoimmune conditions.
Tests that can help check this condition
Learn more on the official NHS page .
