Levothyroxine

NHS medicines information on levothyroxine, including what it's used for, side effects, dosage and who can take it.

What levothyroxine is for

Levothyroxine is mainly used to treat an underactive thyroid (hypothyroidism).

Levothyroxine can help with symptoms of an underactive thyroid including:

• tiredness
• weight gain
• low mood

How to take levothyroxine

Levothyroxine usually comes as tablets or liquid (oral solution) that you swallow.

How much you need to take depends on your thyroid hormone levels, any other conditions you may have and your age. You'll usually take it once a day.

Your doctor may prescribe a low dose to start with and increase it gradually. This is to find the right dose to manage your condition.

You'll usually need to take the medicine for the rest of your life to prevent your symptoms returning. You should be able to live a normal life.

When taking levothyroxine:

• take it on an empty stomach 30 to 60 minutes before your first meal of the day, any drink with caffeine, such as tea or coffee, or any other medicine
• try to take it at the same time each day
• swallow tablets whole with a glass of water
• use the syringe or spoon that comes with the liquid to measure out the correct dose

Always check the packet or leaflet that comes with your medicine. Ask a pharmacist or doctor for advice if you're not sure how to take it or you have any problems taking it.

Side effects of levothyroxine

Like all medicines, levothyroxine can cause side effects, although not everyone gets them.

Most side effects usually happen when the dose is too high. They often improve when the dose is changed.

Common side effects

Common side effects of levothyroxine include:

• difficulty sleeping (insomnia)
• headaches
• feeling anxious
• sweating
• hair loss

Levothyroxine will not usually affect your ability to drive, ride a bike or use machinery.

Who can and cannot take levothyroxine

Most adults and children can take levothyroxine.

But levothyroxine is not suitable for everyone. For example, it may not be suitable if:

• you've had an allergic reaction or serious side effect from levothyroxine
• you have an overactive thyroid
• you have diabetes
• you have a condition that affects your adrenal glands
• you have a heart condition

Check the packet or leaflet that comes with your medicine to see if it's suitable for you. Speak to a pharmacist or doctor if you're not sure if you can use it.

Breastfeeding and levothyroxine

You can usually take levothyroxine while breastfeeding but check with a pharmacist or doctor first.

It's rare for breastfed babies to get any side effects from medicine you're taking, but speak to a healthcare professional if you have any concerns about your baby.

Pregnancy and levothyroxine

Tell your doctor if you're pregnant (or get pregnant) while taking levothyroxine.

Levothyroxine can be taken during pregnancy if needed.

If you need to take levothyroxine while you're pregnant, you may need more blood tests to check your thyroid hormone levels and make sure you're taking the right dose.

Your doctor will talk to you about the risks and benefits of taking it while pregnant.

Taking levothyroxine with other medicines, food and drink

There are some medicines, remedies and supplements that may not mix well with levothyroxine.

These include:

• medicines for epilepsy, such as carbamazepine
• medicines to reduce the amount of acid in your stomach, such as omeprazole
• medicine for weight gain, such as semaglutide
• antidepressants, such as sertraline
• antacids and other indigestion treatments
• calcium and iron supplements
• some medicines for high blood pressure and heart problems, such as beta blockers and digoxin
• the herbal supplement St John's wort
• biotin (vitamin B7) as it can affect your thyroid tests

Before taking levothyroxine, tell your doctor if you're taking any other medicines, herbal remedies, vitamins or supplements.

Food, drink and alcohol with levothyroxine

Taking levothyroxine with some foods can affect how it works. It's best to take it 30 to 60 minutes before your first meal of the day, or any drink with caffeine, such as tea or coffee.