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Treating an overactive thyroid (hyperthyroidism)

Te whakarauora i te mate tenga

woman taking tabletThe treatment options for an overactive thyroid (hyperthyroidism) include medicines, radioactive iodine and surgery. The treatment you'll need depends on the cause of your overactive thyroid and how well it responds to the treatment.

You may also need treatment if you have Graves' eye disease, which affects about one in 20 people who have Graves' disease. If you're experiencing irritation and redness, bulging eyes and double vision, you may need to see an ophthalmologist (specialist eye doctor). Treatment for this may include drops, medicines and rarely surgery.

Medicines for an overactive thyroid

Anti‑thyroid medications like carbimazole reduce the amount of thyroxine that your thyroid produces. They usually take several weeks to bring your levels back to normal.

You often start on a high dose, which can be reduced once your thyroxine levels have dropped. You'll usually keep taking carbimazole for at least 12 to 18 months.

If your thyroid overactivity is due to Graves’ disease, there is about a one in two chance that the overactivity will go away after this time, meaning that you can stop taking carbimazole. If the overactivity doesn't go away, or if the overactivity comes back again in the future, other treatments are usually considered, Some people keep taking carbimazole for several years.

Most people do not get side effects with carbimazole, but it can cause stomach upset, rash and joint pains. Very rarely, you can get a low white blood cell count (fewer white blood cells in your blood). These cells help your body fight infection. If you have a high temperature, sore throat or mouth ulcer, stop taking your thyroid medicine and see a doctor urgently to have a blood test.

You might also need to take a medicine called a beta blocker, like propranolol. This doesn't affect your thyroid but helps with some of the symptoms, such as the shakes (tremor), racing heart (palpitations), and nervousness.

Radioiodine treatment

With radioiodine treatment, you take radioactive iodine as a liquid or capsule. This destroys your thyroid cells. It takes several weeks to be effective and is successful in most people.

This is a very safe and effective treatment. The radiation dose you receive is very small and isn't enough to cause cancer later in life.

You'll need to take precautions for two to three¬†weeks after your treatment while your body clears the low‑dose radiation. This includes limiting close contact with children and pregnant women. Your health professional will advise you to avoid pregnancy for several months after the treatment.

The main side effect of the treatment is that your thyroid may become underactive (hypothyroidism). You'll have blood tests to check for this and it's easily treated with thyroid tablets.


Sometimes people need surgery to remove part or all of their overactive thyroid. Surgery is particularly useful if you have a very large thyroid or if other treatments have not worked.

Thyroid surgery is generally very safe but can have some side effects, such as affecting your calcium balance or damaging your vocal cords.

After surgery, your thyroid may become underactive (hypothyroidism). You'll have blood tests to check for this and it's easily treated with thyroid tablets.

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Written by HealthInfo clinical advisers. Last reviewed July 2023.


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