What is thyroid medicine?

Thyroid medicines are tablets used to treat thyroid gland disorders. The thyroid is a butterfly-shaped gland inside your neck that produces the thyroid hormone.

Thyroid disorders include hypothyroidism, which is when the thyroid is underactive and does not produce enough thyroid hormone. Another thyroid disorder is hyperthyroidism, which is when the thyroid produces too much thyroid hormone. These disorders cause the body's metabolism (natural chemical reactions) to slow down or speed up.

How does thyroid medicine work?

Thyroid medicines work by either replacing missing thyroid hormone, or blocking its production. In hypothyroidism, thyroid medicine replaces the thyroid hormone that the body cannot produce in the right amounts. In hyperthyroidism, thyroid medicine blocks thyroid hormone production, because the body produces too much.

Thyroid medicines are only available with a doctor's prescription. Thyroid medicine should only be used if you have been diagnosed with a thyroid disorder.

What types of thyroid medicine might I be prescribed?

Thyroid medicines are available as tablets, and only with a doctor's prescription.

If you're diagnosed with hypothyroidism, you may be prescribed medicine which replaces the hormones normally produced by the thyroid gland.

Levothyroxine is commonly used to treat hypothyroidism and replaces the hormone T4.

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

There are several different thyroid medicines that can treat hyperthyroidism. They include propylthiouracil and carbimazole.

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

All of these thyroid medicines are available on the Pharmaceutical Benefits Scheme (PBS), however, some brands may cost more than others.

Search your medicines by brand name or active ingredient using the healthdirect Medicines tool.

How do I take thyroid medicine?

Thyroid medicine is usually taken daily, although some people may take their medicine weekly or take a different dose on certain days of the week.

If you have been prescribed levothyroxine by your doctor, it is recommended that you take your dose as soon as you wake up in the morning, and at least 30 - 60 minutes before eating. Other medicines (including supplements) should not be taken at the same time as levothyroxine.

There are several different brands of levothyroxine tablets available in Australia, and it is important that you remember the brand name of your medicine. Not all brands can be substituted for each other, so be sure to let your pharmacist know which brand you take.

Some brands of levothyroxine need to be stored in a fridge — check with your pharmacist to see if this applies to your medicine.

Always tell your doctor, dentist or pharmacist if you are taking medicines to manage a thyroid disorder.

Does thyroid medicine have any side effects or risks associated with it?

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

These are most common 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

Rare but serious side effects include a decrease in white blood cells and liver injury.

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, as you may need a different dose or type of medicine.

Depending on how you respond to the medicine, your doctor may change your dose.

Because some other medicines and vitamins might affect how thyroid medicines work, it is important to let your doctor know about any other medicines you are taking. Tell your doctor about all of your prescription medicines, non-prescription medicines and supplements.

When should I see my doctor?

If you have symptoms of a thyroid disorder or notice changes in your thyroid gland, such as a lump on your neck, it is important to see a doctor. Your doctor will most likely refer you for tests to see if you have a thyroid disorder before you begin treatment.

You should see your doctor if you have been diagnosed with a thyroid disorder and your symptoms are changing or you are experiencing side effects from your thyroid medicine.

Thyroid medicine and pregnancy

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

Your health team will monitor your thyroid disorder regularly during pregnancy, and your doctor may need to adjust the dose or type of thyroid medicine you are using. Some thyroid medicines used to treat hyperthyroidism have been associated with birth defects. For this reason, your doctor may prescribe a different type of thyroid medicine for you to use during pregnancy.

Are there any alternatives to this medicine?

For people with a thyroid disorder, it is important to take the thyroid medicine as prescribed by their doctor.

For some patients with hyperthyroidism, radioactive iodine — which damages and destroys the overactive thyroid cells, or surgery — to remove part of, or all of the thyroid gland may be required. Your thyroid specialist will recommend the most appropriate treatment for you,

Resources and support

• The Australian Thyroid Foundation provides patient education, support and advocacy on thyroid health.
• Call healthdirect on 1800 022 222 at any time to speak to a registered nurse (known as NURSE-ON-CALL in Victoria) for more information and advice about thyroid disorder or thyroid medicines.