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Treatment - Overactive thyroid (hyperthyroidism)

An overactive thyroid (hyperthyroidism) is usually treatable.

You'll normally be referred to an endocrinologist (specialist in hormone conditions) for treatment.

The main treatments are:

  • medication
  • radioiodine treatment
  • surgery

Medication for an overactive thyroid

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

You'll usually need to take the medicine for a month or 2 before you notice any benefit. You may be given another medication called a beta blocker to relieve your symptoms in the meantime.

When your thyroid hormone level is under control, your dose may be gradually reduced and then stopped. But some people need to continue taking medication for several years or possibly for life.

Side effects 

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

  • feeling sick
  • headaches
  • aching joints
  • an upset stomach
  • an itchy rash

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

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


Contact your GP immediately if you get symptoms of fever, sore throat or a persistent cough. They'll do a blood test to check your white blood cell level.

You should avoid getting pregnant while taking carbimazole. Women of childbearing potential must use effective contraception during treatment with carbimazole.

Treatment with carbimazole should only be considered in pregnancy after a benefit-risk assessment with your doctor.

Your contraception choices - sexualwellbeing.ie

Radioiodine treatment

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

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

It can take a few weeks or months for the full benefits to be felt, so you may need to take one of the other medications for a short time.

The dose of radiation you're given is very low, but there are some precautions you'll need to take after treatment:

  • avoid prolonged close contact with children and pregnant women for a few days or weeks
  • women should avoid getting pregnant for at least 6 months
  • men shouldn't father a child for at least 4 months

Radioiodine treatment is not suitable if you're pregnant or breastfeeding. It's also not suitable if your overactive thyroid is causing severe eye problems.

Surgery for an overactive thyroid

Surgery to remove all or part of your thyroid may be recommended if:

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

Removing the entire thyroid gland is normally recommended. This cures an overactive thyroid and means there's no chance of the symptoms coming back.

But as a result, you'll need to take medication for the rest of your life to make up for not having a thyroid. These are the same medications used to treat an underactive thyroid.

Complications from an overactive thyroid

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

Page last reviewed: 14 March 2021
Next review due: 14 March 2024

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