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Levothyroxine

Sounds like 'lee-voe-thye-ROX-een'

Key points about levothyroxine

Levothyroxine is a thyroid hormone, used to treat hypothyroidism.
Levothyroxine is also called Eltroxin® or Synthroid®.
Find out how to take it safely and possible side effects.

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Levothyroxine replaces or provides thyroid hormone when your body can't make enough. This is a condition called hypothyroidism. Levothyroxine is also used to treat other types of thyroid disorders, eg, certain types of goiters and thyroid cancer. Read more about hypothyroidism.

In Aotearoa New Zealand levothyroxine is available as tablets in different strengths (25 micrograms, 50 micrograms and 100 micrograms) and different brands (eg, Eltroxin®, Synthroid®, Mercury Pharma®). These brands are all slightly different, so it’s important that you stay on the same brand if possible. If your tablets look different from usual, check with your pharmacist.

May 2024: The appearance of Eltroxin® tablets are changing

Eltroxin® 50 mcg and 100 mcg (levothyroxine), will look different, but will work the same way. It's being made in the same place, with the same ingredients, as the old one. There is the same amount of active ingredient (medicine) in each tablet.

Eltroxin® 100 mcg tablets

New look: From August, the new tablets will be available. They are smaller because there are fewer inactive ingredients in the tablet. The tablet shape and tablet imprint has also changed, so it will look a little different. Learn more about inactive ingredients.
Blood tests: Your doctor may ask you to have a blood test 6 weeks after changing to the new 100 mcg tablets.
More information: Talk to your doctor or pharmacist about what these changes mean for you.

Eltroxin 100 mcg tablets

Eltroxin® 50 mcg tablets

New look: From June, the new tablets will be available. They are the same size but the tablet shape and tablet imprint will change, so it will look a little different.
Blood tests: Since the active (medicine) and inactive ingredients are the same as the old tablets, it's unlikely you will need a blood test.
More information: Talk to your doctor or pharmacist about what these changes mean for you.

For more detailed information about this change, see Your Eltroxin® is changing(external link).

The dose of levothyroxine will be different for different people. It depends on your medical condition, laboratory test results and your response to treatment.
Your doctor will usually start you on a low dose and increase the dose depending on how you respond.
The usual starting dose is 50 to 100 micrograms daily, which may be increased slowly to 100 to 200 micrograms daily.
Levothyroxine is usually taken once a day.
Always take your levothyroxine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much levothyroxine to take, how often to take it and any special instructions.

Timing: Levothyroxine is best taken on an empty stomach, 1 hour before food or 2 hours after food. Try to take it at the same time each day. If you keep forgetting to have it on an empty stomach, and you end up missing your medicine, it's better to just take it at the time that suits you best, and your doctor can increase the dose if needed. Talk to your doctor about this.
Taking other medicines at the same time: Taking some medicines (eg, antacids, iron or iodine containing products) at the same time, can reduce the effect of levothyroxine. Don’t take antacids, iron or iodine containing products within 4 hours of taking this medicine.
Missed dose: If you forget to take your dose, take it as soon as you remember. But if it's nearly time for your next dose, just take the next dose as usual. Don't take 2 doses to make up for a missed dose.
Keep taking levothyroxine regularly: It takes a few weeks before you feel the full effects of levothyroxine. Don't stop taking levothyroxine suddenly, talk to your doctor or nurse before stopping. Levothyroxine treatment is usually lifelong.

Different brands: There are different brands of levothyroxine tablets. It's best to continue taking the same brand of tablets. If you have any questions about the brand you're taking, or if your tablets look different to your last supply, ask your doctor or pharmacist for advice.
Different strengths: Levothyroxine tablets are available in different strengths. If your tablets look different to your last supply, ask your doctor or pharmacist for advice.
Blood tests: You'll need blood tests while taking levothyroxine to check how well the medicine is working for you.
Other medicines: Levothyroxine may interact with other some other medicines, herbal supplements and Rongoā Māori, so check with your doctor or pharmacist before starting levothyroxine and before starting any new products.

Like all medicines, levothyroxine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects	What should I do?
Hair loss	This usually happens during the first few months of treatment and should stop once your body gets used to the medicine. Tell your doctor if this continues or gets worse.
Feeling sick or nausea Headache	Tell your doctor if these bother you.
Feeling restless Increased sweating Feeling flushed or hot Feeling nervous or mood swings Diarrhoea (runny poos) Increased appetite Having trouble sleeping	Tell your doctor.
Signs of an allergic reaction such as skin rash, itching, blisters, peeling skin, swelling of your face, lips or mouth or having problems breathing	Tell your doctor immediately or phone Healthline 0800 611 116.
Fast or irregular heart beat Chest pain Shortness of breath Difficulty breathing	Tell your doctor immediately or phone Healthline 0800 611 116.