Levothyroxine

Levothyroxine can be taken by adults and children. However, levothyroxine is not suitable for some people.

Do not take levothyroxine, but go back to your doctor to discuss your treatment if you have:

• had an allergic reaction to levothyroxine or any other medicines in the past
• an overactive thyroid (hyperthyroidism)
• a health problem that affects your adrenal glands (your doctor will be able to tell you if you are not sure)

Check with your doctor before taking levothyroxine if you have:

• a heart problem including angina, heart disease or heart failure
• high blood pressure
• had a heart attack
• diabetes – the dose of your diabetes medicine may need to change because levothyroxine can raise blood sugar levels

Pregnancy and breastfeeding

Levothyroxine and pregnancy

Levothyroxine is usually safe to take in pregnancy. It is important to carry on taking levothyroxine throughout your pregnancy. Having too low or too high levels of thyroid hormone in pregnancy can cause problems for you and your baby.

You will need to have regular blood tests during pregnancy to make sure you are on the right dose of levothyroxine for you and your baby. Most women need to take a higher dose of levothyroxine than usual while they are pregnant.

Levothyroxine and breastfeeding

It is usually safe to breastfeed while you are on levothyroxine. Thyroid hormones pass into breast milk in very low levels that are too small to affect the baby.

Take levothyroxine once a day, ideally at least 30 minutes before having breakfast or a drink containing caffeine, like tea or coffee.

Food and caffeinated drinks can both stop your body from taking in levothyroxine properly so it does not work as well. If you stop taking levothyroxine your symptoms are likely to come back.

Dosage

You may need to take several different tablets to make up your dose. Levothyroxine comes in 25 microgram, 50 microgram and 100 microgram tablets. The word microgram is sometimes written with the Greek symbol μ followed by the letter g (μg). A microgram is 1,000 times smaller than a milligram (mg).

Your doctor will tell you how many tablets to take each day. The dose of levothyroxine varies from person to person.

Although starting doses are usually the same, the dose of levothyroxine you end up taking or how quickly the dose is increased depends on your symptoms, hormone levels, age and whether you have any other health problems.

Adults usually start with a dose between 50 micrograms and 100 micrograms taken once a day. This may be increased gradually over a few weeks to between 100 micrograms and 200 micrograms taken once a day.

How to take levothyroxine 

Swallow the tablets whole with a drink of water.

Levothyroxine is available as a liquid for children and people who find it difficult to swallow tablets.

If you or your child are taking levothyroxine as a liquid, it will usually be made up for you by the pharmacist. It will come with a plastic syringe or spoon to help you measure out the right dose. If you do not have a syringe or measuring spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not give the right amount.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it is almost time for your next dose in which case just skip the forgotten dose. Do not take 2 doses together to make up for a missed dose.

If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

Taking an extra dose of levothyroxine by accident is unlikely to harm you.

Speak to your doctor if:

• you accidentally take more than 1 extra dose
• you get side effects such as a racing heart beat or chest pain. These symptoms may not happen straight away, it can be several days before they come on

Blood tests

Your doctor will do regular blood tests to check the levels of thyroid hormones in your body before and after starting levothyroxine.

These will allow your doctor to adjust the dose to suit you.

At the start of treatment, you can expect to have blood tests often. Once your hormone levels are stable, you will usually have a blood test after 4 to 6 months, and after that once a year.

You may need blood tests more often if:

• you are pregnant
• you start or stop a medicine that can interfere with levothyroxine
• you have any symptoms that could mean your dose is not quite right

Like all medicines, levothyroxine can cause side effects, although not everyone gets them. Once you are on the right dose of levothyroxine, side effects should go away.

Common side effects and self-help advice

The common side effects of levothyroxine usually happen because the dose you are taking is more than you need. These side effects usually go away after you go on to a lower dose of levothyroxine or stop treatment.

Common side effects are the same as the symptoms of an overactive thyroid. Talk to your doctor or pharmacist if these side effects bother you or do not go away.

Some common side effects include;

• Feeling sick
• Being sick (vomiting) or diarrhoea
• Headaches
• Feeling restless or excitable, or problems sleeping
• Flushing or sweating
• Muscle cramps
• Shaking, usually of the hands

Serious side effects

Serious side effects rarely happen, but some people may have serious side effects when taking levothyroxine.

Call a doctor straight away if you get:

• chest pain
• fast or irregular heartbeats, or palpitations
• Serious allergic reaction

In rare cases, it is possible to have a serious allergic reaction (anaphylaxis) to levothyroxine.

Cautions with other medicines

Some medicines can interfere with thyroid hormones, hence a need to change the dose of levothyroxine. These medicines include:

• medicines for fits or seizures – such as carbamazepine and phenytoin
• rifampicin
• amiodarone
• oestrogens – such as in combined contraceptive pills or hormone replacement therapy (HRT)

Levothyroxine can change how other medicines work, so their doses may need to be altered. These medicines include:

• medicines for diabetes – either insulin or tablets
• the blood thinning medicine, warfarin

Some medicines should not be taken at the same time of the day as levothyroxine as they can reduce the amount of levothyroxine your body takes in. These medicines include:

• antacids
• calcium salts
• iron salts
• orlistat, a medicine used for weight loss
• sucralfate, a medicine used to treat stomach ulcers
• some cholesterol-lowering medicines such as cholestyramine, colestipol or colesevelam

Mixing levothyroxine with herbal remedies and supplements

There is very little information about taking herbal remedies and supplements with levothyroxine.

How does levothyroxine work?

The thyroid gland in your neck makes a hormone called thyroxine. Thyroxine controls how much energy your body uses (the metabolic rate). It is also involved in digestion, how your heart and muscles work, brain development and bone health.

When the thyroid gland does not make enough thyroxine (a condition called hypothyroidism), many of the body’s functions slow down. Some of the most common symptoms of an underactive thyroid gland are:

• tiredness
• feeling cold
• difficulty concentrating
• weight gain

How long does levothyroxine take to work?

Levothyroxine starts working straight away, but it may be several weeks before your symptoms start to improve and you feel any different.

How long will I take levothyroxine for?

Treatment with levothyroxine is usually lifelong. If you stop taking levothyroxine your symptoms are likely to come back.

Is levothyroxine safe to take for a long time?

Yes, it is safe to take levothyroxine for a long time, even many years. High doses of levothyroxine over a long time can sometimes cause weakening of the bones (osteoporosis).

This should not happen if you are on the right dose. It is important to have regular blood tests to make sure your dose is not too high.

Will it affect my fertility?

There is no clear evidence to suggest that taking levothyroxine will reduce fertility in either men or women.

However, speak to a pharmacist or your doctor if you are trying to get pregnant. They may want to review your treatment.

Can I drink alcohol with it?

Yes, you can drink alcohol while taking levothyroxine. Alcohol does not affect how this medicine works.

Will it make me lose weight?

One of the symptoms of an underactive thyroid gland is weight gain. Once you start taking levothyroxine, you may lose weight as your body’s hormones rebalance. Losing weight can also be a sign that your dose of levothyroxine is too high.

Once your thyroid hormone levels have returned to normal, your tendency to gain or lose weight is the same as for people who do not have thyroid problems.

Can I drive or ride a bike with it?

Yes, levothyroxine should not affect your ability to drive or ride a bike.

Is there any food or drink I need to avoid?

There are some foods and drinks that do not mix well with levothyroxine:

• Drinks containing caffeine, like coffee, tea and some fizzy drinks, can reduce the amount of levothyroxine your body takes in. Leave at least 30 minutes after taking levothyroxine before you drink them.
• Calcium-rich foods, such as milk, cheese, yoghurt and broccoli, can reduce the amount of levothyroxine your body takes in. Leave at least 4 hours between taking levothyroxine and eating calcium-rich foods.
• Soya in food and supplements may stop levothyroxine working properly. If you regularly eat soya or take soya supplements your doctor might need to do extra blood tests to make sure you are getting enough levothyroxine.
• Kelp (a type of seaweed) can contain high levels of iodine, which sometimes makes an underactive thyroid worse.

Will it affect my contraception?

Contraceptive pills that contain oestrogen (combined contraceptive pills) can reduce the amount of levothyroxine in your body.

Will I lose my hair?

It is having an underactive thyroid that causes hair loss and not treatment with levothyroxine.

Because the natural hair growth cycle takes several months, hair loss related to thyroid disease might only be seen months after the illness has begun. If treatment with levothyroxine has already started, it may seem like the medicine – rather than the underlying illness – is causing the hair loss.