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Treatment - Overactive thyroid (hyperthyroidism)

You will usually be referred to an endocrinologist (specialist in hormone conditions) for treatment.

There are different types of treatment for an overactive thyroid (hyperthyroidism).

The main treatments are:

  • medicine
  • radioiodine treatment
  • surgery

Medicine for an overactive thyroid

The most common medicines used to treat an overactive thyroid are carbimazole and propylthiouracil. These stop your thyroid producing too much thyroid hormones.

It may take 1 to 2 months before you notice any benefit from the medicine. Your doctor will sometimes give you medicine called a beta blocker for a short time. This can help relieve your symptoms.

When your thyroid hormone level is under control, your doctor may gradually reduce the dose and then stop it. But some people need to take medicine for years or possibly for life.

Side effects

During the first couple of months, some people have the following side effects:

These should pass as your body gets used to the medicine.

A less common but more serious side effect is a sudden drop in your white blood cell level (agranulocytosis). This can mean you're vulnerable to infections.

Urgent advice: Contact your GP for an urgent appointment if you have:

  • symptoms of fever
  • sore throat
  • persistent cough

They'll do a blood test to check your white blood cell level.

Avoid getting pregnant while taking carbimazole. If you can get pregnant and are taking carbimazole, use contraception.

Your doctor may prescribe propylthiouracil instead of carbimazole during pregnancy. Or they may prescribe carbimazole. They will assess the benefits and risks of using this medicine and discuss these with you.

Problems in pregnancy

Your contraception choices -

Radioiodine treatment

Radioiodine treatment is where radiation is used to damage your thyroid. This reduces the amount of hormones it can produce. It can cure an overactive thyroid.

How radioiodine treatment works

You're given a drink or capsule that contains a low dose of radiation. This is absorbed by your thyroid. Most people only need a single treatment.

It can take a few weeks or months to notice the full benefits of the treatment. You may need to take another medicine for a short time.

The dose of radiation you're given is very low. But there are some precautions you need to take after treatment.


  • do not spend much time with children and pregnant women, for a few days or weeks

  • do not get pregnant for at least 6 months

  • do not father a child for at least 4 months

Radioiodine treatment is not suitable if:

  • you're pregnant
  • breastfeeding
  • have severe eye problems from an overactive thyroid

Surgery for an overactive thyroid

You may need to have surgery to remove all or part of your thyroid.

You may need surgery if:

  • your thyroid gland is severely swollen
  • you have severe eye problems from an overactive thyroid
  • you cannot have any of the other treatments
  • your symptoms come back after trying other treatments

You will usually have all of your thyroid removed. This cures an overactive thyroid and means there's no chance of the symptoms coming back.

But you will need to take hormone replacement medicine for the rest of your life.

Complications from an overactive thyroid

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 20 December 2023
Next review due: 20 December 2026

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.