Levothyroxine is a replacement or supplement thyroid hormone.
You will need regular blood tests to check your thyroid levels, particularly at the beginning of your treatment.
If you experience any side-effects, speak with your doctor as your dose may need adjusting.
|Type of medicine||Thyroid hormone|
|Used for||Underactive thyroid gland (hypothyroidism)|
|Also called (UK)||Eltroxin®|
|Also called (USA)||Levoxyl®; Levo-T®; Synthroid®; Tirosint®; Unithroid®|
Combination brand: NP Thyroid® (levothyroxine with liothyronine)
|Available as||Tablets and oral liquid medicine|
If you have an underactive thyroid gland, it means that your thyroid gland does not produce enough thyroid hormone. This is a condition known as hypothyroidism. Levothyroxine (which is also called levothyroxine sodium) restores the balance of thyroid hormone in your body. It is very similar to thyroxine, the hormone which your body produces naturally.
Before taking levothyroxine
Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking levothyroxine it is important that your doctor knows:
- If you are pregnant or breastfeeding. This is so your doctor can keep a check on your baby.
- If you have a heart problem such as heart failure or angina, or if you have high blood pressure (hypertension).
- If you have ever been told your adrenal gland is unable to produce enough of the hormone cortisol, a condition called adrenal insufficiency.
- If you have been told your thyroid is overactive (producing too much thyroxine).
- If you have high levels of sugar (glucose) in your blood (diabetes mellitus)
- If you have been told you have a problem regulating the levels of water in your body, a rare condition known as diabetes insipidus.
- If you have epilepsy.
- If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
- If you have ever had an allergic reaction to a medicine.
How to take levothyroxine
- Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The manufacturer's leaflet will give you more information about levothyroxine and a full list of the side-effects which you may experience from taking it.
- Take levothyroxine exactly as your doctor tells you to. Your doctor will ask you to take one dose each day, preferably before your breakfast. The number of tablets you need to take for each dose will be adjusted to suit you.
- There are three strengths of tablet (25 micrograms, 50 micrograms and 100 micrograms) and your dose may be a combination of different-strength tablets.
- As a guide, it is usual for adults to start by taking a daily dose of 50-100 micrograms, and for this to be increased gradually to a daily dose of 100-200 micrograms. Your doctor or pharmacist will tell you what dose is right for you.
- If levothyroxine has been prescribed for a child, the doctor will tell you what dose to give. The dose for children depends upon their weight, age and what they are being treated for. Give levothyroxine to your child at least half an hour before they eat their first meal of the day.
- Most people find that levothyroxine tablets are easily swallowed. If you do have swallowing difficulties, some brands of tablet can be added to a little water and allowed to disperse before swallowing. Ask your pharmacist to check if your brand of tablet will disperse in water. Alternatively, ask your doctor to prescribe the oral liquid medicine for you.
- If you forget to take a dose, take it as soon as you remember, if it is still within two or three hours of your usual time. If it is longer than this before you remember, skip the forgotten dose. Do not take two doses together to make up for a missed dose.
Getting the most from your treatment
- Try to keep your regular appointments with your doctor so your progress can be monitored. You will need regular blood tests to check your thyroid levels, particularly in the early stages of your treatment.
- If you buy any medicines, check with a pharmacist that they are safe to take with levothyroxine. Levothyroxine should not be taken at the same time as indigestion remedies or preparations containing calcium or iron (which are contained in some vitamin products). These types of medicines reduce the amount of levothyroxine absorbed by your body. Leave at least two hours between taking your dose of levothyroxine and any such preparation.
- Calcium or iron found in the food you eat can also reduce the amount of levothyroxine absorbed by your body. Try to take your dose at least 30 minutes before your first meal of the day.
- If you have diabetes you may need to check your blood glucose more frequently, as levothyroxine may affect the levels of sugar in your blood. Your doctor will be able to advise you about this.
- If you are having an operation or dental treatment, tell the person carrying out the treatment that you are taking levothyroxine.
- Treatment with levothyroxine is usually lifelong. Continue to take this medicine unless your doctor tells you to stop.
Can levothyroxine cause problems?
Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the ones associated with levothyroxine. You will find a full list in the manufacturer's information leaflet supplied with your medicine. Experiencing side-effects may be an indication that your dose needs adjusting, so speak with your doctor if you experience any of the symptoms listed below.
|Levothyroxine side-effects||What can I do if I experience this?|
|Feeling sick (nausea) or being sick (vomiting)||Stick to simple foods - avoid rich or spicy meals|
|Diarrhoea||Drink plenty of water to replace lost fluids|
|Headache||Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the headaches continue, speak with your doctor|
|A feeling that your heart is pounding (palpitations) or chest pain||Let your doctor know about this as soon as possible|
|Feeling restless, feeling flushed, feeling hot, sweating, difficulty sleeping, loss of weight, muscle cramps, temporary loss of hair, itchy rash, menstrual changes||Discuss these with your doctor|
If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.
How to store levothyroxine
- Keep all medicines out of the reach and sight of children.
- Store in a cool, dry place, away from direct heat and light.
Important information about all medicines
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.
This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
If you have any questions about this medicine ask your pharmacist.
Further reading and references
Manufacturer's PIL, Eltroxin® 50 and 100 micrograms Tablets; ADVANZ Pharma (formerly Concordia International), The electronic Medicines Compendium. Dated November 2019.
British National Formulary, 79th Edition (Mar 2020); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.