An underactive thyroid (hypothyroidism) slows the body's metabolism. It develops gradually, so the early signs are easy to put down to stress or ageing.
Common signs
Persistent tiredness, weight gain, feeling cold, constipation, dry skin, hair thinning, low mood and heavier or irregular periods are the most common. Not everyone has all of them, and many of these have other causes.
How it is tested
A simple blood test, usually TSH with thyroid hormone levels, confirms the diagnosis. Your doctor may add antibody tests or a scan if there is a swelling or nodule.
Treatment
Treatment is usually a daily thyroid hormone tablet, taken on an empty stomach. The dose is adjusted by blood tests, so regular follow-up matters. Do not start, stop or change the dose without medical advice, especially during pregnancy.
