Hyperthyroidism

Key facts

• Hyperthyroidism happens when the thyroid gland makes more hormone than the body needs, speeding up metabolism and affecting nearly every organ system.
• Common signs are a fast or irregular heartbeat, unexplained weight loss despite a good appetite, feeling hot, anxiety, trembling hands and disturbed sleep; bulging eyes can point to Graves' disease, the most common cause.
• First-line treatment is an antithyroid medicine, carbimazole or thiamazole, usually taken for twelve to eighteen months while levels normalise.
• Seek prompt care for a very fast heartbeat, or a fever with a sore throat, while taking antithyroid treatment.

What the overactive thyroid feels like

The signs come on gradually and are easy to dismiss early. A persistently fast or irregular heartbeat, unexplained weight loss despite a good appetite, and feeling hot when others do not are the classic cluster. Anxiety, trembling hands, loose stools and disturbed sleep are also common. In some people the eyes appear wider or begin to protrude, a feature linked to Graves' disease, the most frequent underlying cause.

Bringing hormone levels down

Antithyroid medicines are usually the first approach. They work by blocking the thyroid's ability to make new hormone. Carbimazole and thiamazole are the two most widely used; carbimazole converts to thiamazole in the body, so both act through the same mechanism. Treatment typically runs for twelve to eighteen months, with the dose adjusted as levels normalise. The broader thyroid category covers other options when antithyroid medicine alone is not enough to control levels.

When to see a doctor

If your heartbeat becomes very fast, or you develop a fever with a sore throat while taking antithyroid treatment, get medical attention promptly. Rarely, these medicines affect white blood cell counts and need urgent assessment. Ongoing symptoms despite treatment, or eye changes that worsen, also warrant a review.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.