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Condition

Hypothyroidism

A condition in which the thyroid does not produce enough hormone, slowing many body processes.

Hypothyroidism means the thyroid is underactive - it is not making enough T4 and T3 to meet the body's needs. With less thyroid hormone available, many processes slow down.

Common symptoms include persistent fatigue, weight gain, feeling cold, constipation, dry skin and brittle hair, low mood or depression, impaired memory and concentration, slow heart rate, and muscle aches. Symptoms often develop gradually over months and may be subtle at first.

The most common cause in the UK is Hashimoto's thyroiditis (autoimmune). Other causes include previous thyroid surgery or radioactive iodine treatment, certain medicines (such as lithium or amiodarone), iodine deficiency (uncommon in the UK), and, rarely, pituitary problems.

Diagnosis is confirmed by a raised TSH - the pituitary working harder to stimulate a flagging thyroid - combined with a free T4 below the reference range. Treatment is with levothyroxine tablets, which replace the hormone the thyroid can no longer make in sufficient quantities.

Common questions

How is hypothyroidism treated?
Usually with a daily levothyroxine tablet. The dose is adjusted gradually, guided by TSH and free T4 blood tests, until levels return to the reference range. Your GP or specialist manages this.
Can hypothyroidism be cured?
In most cases it is a lifelong condition managed with daily medication rather than cured. Some causes (such as postpartum thyroiditis) are temporary, so your doctor will re-test to clarify the picture.
Why do some people still feel unwell on levothyroxine?
This is not fully understood. Some people have persistent symptoms even when blood tests are normal. It is worth discussing honestly with your GP or endocrinologist - there are options worth exploring together.

Related terms

TSH (thyroid-stimulating hormone) Free T4 (free thyroxine) Hashimoto's thyroiditis Levothyroxine Subclinical hypothyroidism

ThyroidTools is an independent, patient-led project - not a charity, not a medical service, and not affiliated with any healthcare organisation or clinical body. We're not your doctor. We're the friend who helps you get more from seeing one. Nothing here is medical advice; always speak to a qualified clinician about your own situation.