Medicines for Overactive thyroid (hyperthyroidism)

What it is

The thyroid is a small gland in the neck that makes hormones controlling the body's metabolism. In an overactive thyroid it makes too much, and body processes speed up, causing symptoms such as a fast or irregular heartbeat, weight loss despite a good appetite, feeling hot and sweaty, tremor, anxiety, restlessness, loose bowels and difficulty sleeping. The commonest cause in the UK is Graves' disease, an autoimmune condition in which the immune system stimulates the gland and which can also affect the eyes; other causes include overactive thyroid nodules. Diagnosis rests on blood tests showing raised thyroid hormones with a suppressed thyroid-stimulating hormone (TSH), and further tests help identify the cause. Left untreated, a persistently overactive thyroid can strain the heart — it is a recognised cause of atrial fibrillation — and weaken the bones, which is why it is important to treat.

How it is treated

Treatment has two parts: reducing the excess thyroid hormone, and easing symptoms while that takes effect. Antithyroid medicines lower the gland's production of hormone and are often the first step, used either as a course in their own right or to settle things before a more definitive treatment. Many people are offered a more permanent option — radioactive iodine, which gradually shrinks the overactive tissue, or surgery to remove part or all of the gland — with the choice depending on the cause, the size of the gland, eye involvement, pregnancy plans and personal preference. Because these definitive treatments can leave the thyroid underactive, hormone replacement is often needed afterwards. A particular safety point with the antithyroid medicine carbimazole is a rare but serious drop in white blood cells, so a sore throat, mouth ulcers, fever or signs of infection should prompt an urgent blood check and stopping the medicine until advised. Care is usually shared with a specialist, with regular blood tests to guide treatment.