Underactive thyroid (hypothyroidism)
An underactive thyroid is when the thyroid gland does not make enough hormones. It is common, easily diagnosed with a blood test, and usually treated with daily tablets.
- Updated August 2026
- Clinical review pending
- 1 source
At a glance
- An underactive thyroid does not make enough thyroid hormone.
- It is diagnosed with a simple blood test.
- It is usually treated with daily levothyroxine tablets, often for life.
On this page (5 sections)
Overview
An underactive thyroid (hypothyroidism) is when the thyroid gland — in the neck — does not produce enough hormones. This can slow down parts of the body and cause a range of symptoms [1].
Symptoms
Symptoms often develop slowly and can include tiredness, feeling cold, weight gain, constipation, low mood, and dry skin. Because these are common and can have other causes, a blood test is used to check [1].
Causes
In the UK the most common cause is a problem with the immune system. It can also happen after some treatments for the thyroid, and it can run in families [1].
Treatment
It is treated with a daily tablet called levothyroxine, which replaces the missing hormone. Most people need to take it for life, with regular blood tests to check the dose is right [1]. Do not change the dose without advice.
When to see a doctor
See a GP if you have symptoms that could be an underactive thyroid, so a blood test can be arranged [1].
Sources
- NHS. Underactive thyroid (hypothyroidism) (opens in new tab) Last reviewed 28 April 2025. Accessed 12 August 2026.
About this page
- Written by
- Consumer Health editorial team
- Medical review
- Pending — this page has not yet been reviewed by a named clinician. Read our medical review policy.
- Last updated
- August 2026
- Next review due
- August 2027
Important: This information is for general guidance only and does not replace professional medical advice. It is not intended to diagnose or treat any condition. Always speak to a qualified healthcare professional — such as your GP or pharmacist — for advice about your individual circumstances, and do not start, stop or change any prescribed treatment based only on this page. If you think you are having a medical emergency, call 999. Consumer Health is an independent health-information resource and is not the NHS or a government body.
Was this page helpful?Your feedback helps us improve.