What is thyroid medicine?

Thyroid medicines are tablets used to treat thyroid gland disorders. Your thyroid is a butterfly-shaped gland in your neck that makes thyroid hormone.

Thyroid disorders include hypothyroidism and hyperthyroidism.

Hypothyroidism is when your thyroid is underactive and does not produce enough thyroid hormone. This disorder makes your body's metabolism (natural chemical reactions) slow down.

Hyperthyroidism is when your thyroid produces too much thyroid hormone. This disorder makes your body's metabolism speed up.

Thyroid medicines are also used to manage thyroid cancer.

How does thyroid medicine work?

Thyroid medicines work by either replacing missing thyroid hormone or blocking its production.

If you have hypothyroidism, your thyroid medicine replaces thyroid hormone because your body doesn't produce enough. If you have hyperthyroidism, your thyroid medicine blocks thyroid hormone production, because your body produces too much.

It can take 4 to 6 weeks for thyroid hormone replacement medicines to start fully working. Your doctor may need to change your dose to find the best amount for you to take.

Thyroid medicines are only available with a doctor's prescription. You should only take thyroid medicine if your doctor has diagnosed you with a thyroid disorder.

What types of thyroid medicine are available?

Thyroid medicines are available as tablets. You need to get them from a pharmacy with a doctor's prescription.

Medicines for an underactive thyroid

If you have hypothyroidism, you may need a medicine which replaces the hormones normally produced by the thyroid gland.

Levothyroxine is a medicine used to treat hypothyroidism. It replaces the hormone T4.

Liothyronine replaces the hormone T3. It is usually only prescribed after careful consideration by a thyroid specialist (endocrinologist).

Medicines for an overactive thyroid

There are several different thyroid medicines that can treat hyperthyroidism. They include:

• propylthiouracil
• carbimazole

These medicines work by blocking the production of hormones in your thyroid gland.

Cost of thyroid medicines

All of these thyroid medicines are available on the Pharmaceutical Benefits Scheme (PBS). However, some brands may cost more than others. Ask your pharmacist to explain what you need to pay.

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What are the possible side effects or risks of thyroid medicine?

Side effects of thyroid medicines are rare, so long as you are taking the correct dose.

If you are taking thyroid medicines to treat hypothyroidism, side effects can include:

• tiredness
• increased appetite
• diarrhoea
• feeling nervous
• a racing heart
• trouble sleeping
• decreased bone density

These are more likely to happen if the medicine dose is too high.

If you are taking thyroid medicines to treat hyperthyroidism, common side effects include:

• nausea
• vomiting
• stomach discomfort
• rash and itching
• headache

Rare but serious side effects of medicines for hyperthyroidism include:

• a decrease in your number of white blood cells
• liver injury
• birth defects

Tell your doctor immediately if you're taking thyroid medicine and have any of the following side effects:

• fever
• mouth ulcers
• sore throat
• rash
• severe fatigue
• nausea
• abdominal pain
• yellowing skin or eyes (jaundice)

If you are experiencing side effects from thyroid medicine, it is important to see your doctor. You may need a different dose or a different type of medicine.

Depending on how you respond to the medicine, your doctor may change your dose. You may need to have a thyroid function blood test to check you are on the right dose.

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How do I take thyroid medicine?

It's important to take your thyroid medicine exactly as your doctor tells you.

You will probably need to take your thyroid medicine once a day. However, your doctor may suggest a medicine that you need to take once a week. Some people need to take a different dose on certain days of the week.

If you are on levothyroxine, it is usually best to take your dose as soon as you wake up in the morning. Take it at least 30 - 60 minutes before eating breakfast. Avoid taking other medicines (including supplements) at the same time as levothyroxine.

There are several different brands of levothyroxine tablets available in Australia. It's important that you remember or write down the brand name of your medicine. Not all brands can be substituted (swapped) for each other, so make sure your pharmacist knows which brand you use.

You might need to store levothyroxine in the fridge. Some brands have different storage instructions to others. Check with your pharmacist how to store your medicine.

Taking other medicines with thyroid medicines

Before starting on thyroid medicines, tell your doctor about any other medicines you take. This is because some medicines, vitamins and minerals affect how well thyroid medicines work.

Tell your doctor about:

• prescription medicines
• non-prescription medicines
• over-the-counter medicines
• supplements or vitamins

Always tell your doctor, dentist or pharmacist if you are taking medicines to manage a thyroid disorder. If you are having elective surgery, tell your surgeon about your thyroid medicines.

Are there any alternatives to thyroid medicine?

If you have a thyroid disorder, it's important to take your thyroid medicine as prescribed.

Some patients with hyperthyroidism are treated with radioactive iodine. This treatment works by damaging the overactive thyroid cells. Some people will need to have surgery to remove part of, or all of, their thyroid gland. Your thyroid specialist or endocrinologist will recommend the most appropriate treatment for you.

If your diet is low in iodine, taking a supplement can help prevent hypothyroidism. Supplements do not help if you have high thyroid hormone levels.

When should I see my doctor?

See your doctor if you have symptoms of a thyroid disorder or notice changes in your thyroid gland, such as a lump on your neck. Your doctor will be able to organise tests to see if you have a thyroid disorder.

See your doctor if you have a thyroid disorder and your symptoms change. Tell your doctor if you experience side effects from your thyroid medicine.

Thyroid medicine and pregnancy

You should have your thyroid disorder monitored by a doctor if you are planning to become pregnant, are pregnant or are breastfeeding. This is because pregnancy may affect your thyroid gland.

Your healthcare team will monitor your thyroid disorder regularly during pregnancy. Your doctor may need to adjust the dose or type of thyroid medicine you are using. Some medicines used to treat hyperthyroidism can lead to an increased chance of your baby having a birth defect. For this reason, your doctor may prescribe a different type of thyroid medicine for you to use during pregnancy.

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Resources and support

You can find out more about thyroid conditions and medicines.

• The Australian Thyroid Foundation provides patient education, support and advocacy on thyroid health.
• The Hormones Australia website describes thyroid problems including hypothyroidism and hyperthyroidism. They also have a information about how to Find an Endocrinologist.
• The Queensland Health My Amazing Body series includes a podcast about the thyroid gland.
• Learn about the Pharmaceutical Benefits Scheme (PBS)

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.