Thyroid Gland
A butterfly-shaped neck gland producing hormones that set the body's metabolic rate.
What it means
The thyroid sits in the front of the neck and produces thyroxine (T4) and triiodothyronine (T3), hormones that regulate the rate at which the body uses energy.
Its output is controlled by TSH from the pituitary gland, in a feedback loop.
- Hypothyroidism — underactivity. Fatigue, weight gain, cold intolerance, constipation, low mood
- Hyperthyroidism — overactivity. Weight loss, palpitations, tremor, heat intolerance, anxiety
Both are common, particularly in women, and both are treatable.
In practice
Thyroid nodules are frequently found incidentally on neck imaging and are usually benign. A diffusely enlarged thyroid is a goitre.
Antibody tests identify autoimmune thyroid disease, the commonest cause in the UK.
Why it matters
Thyroid symptoms are non-specific and easily attributed to stress, ageing or the menopause, which is why testing is worthwhile when the picture fits.
Thyroid function should be checked during pregnancy and in anyone planning it, as untreated hypothyroidism affects fetal development.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026