Carbamazepine

How it works

What does carbamazepine do?

Carbamazepine is a type of medicine called a ‘mood stabiliser’ as it controls feelings of excitability and over-activity. It can also help with periods of low mood.

Carbamazepine is usually only prescribed after you have already tried other mood stabilisers such as lithium, olanzapine and valproate.

Carbamazepine can help to calm down the brain. There are gateways in the brain called ‘sodium channels’, which can be open or closed. When they are open, there is more electrical activity in the brain. Carbamazepine locks on to closed sodium channels and keeps them closed. Reduced electrical activity leads to reduced release of chemical transmitters that excite the brain, which lowers the amount of glutamate, dopamine and noradrenaline circulating around the brain.

How long does carbamazepine take to start working?

It should only take a few days for carbamazepine to start helping.

Your doctor might start you on a low first dose, and then bring it up to your normal dose to reduce the chance of side effects.

The effect will build over the first one to two weeks. It will take a few weeks at your normal dose for carbamazepine to show its full effect.

How long will I need to take carbamazepine for?

Most people take carbamazepine for at least six months.

You and your doctor should talk about how long you need to take carbamazepine before you start your treatment.

You might have to change your dose to get the best effect for you.

If you only get ill every 12 months you will probably need to take it for longer than 12 months to get any benefit.

Your doctor needs to know if...

You need to talk to your doctor or pharmacist before you take carbamazepine if you think you may be allergic to carbamazepine (or similar medicines like oxcarbazepine (Trileptal™)), tricyclic antidepressants like amitriptyline, or an epilepsy medicine called phenytoin.

You also need to talk to your doctor or pharmacist before starting treatment with carbamazepine if any of the following apply to you:

• you have any heart or liver problems
• you have ever had problems with your bone marrow
• you have a blood problem called porphyria
• you are from a Han Chinese or Thai family background (certain reactions to this medicine are more likely in people of these origins – your doctor will want to check if you’re at risk of this problem by doing a blood test)
• you have taken drugs called monoamine oxidase inhibitors (MAOIs), used to treat depression, within the last 14 days
• you are pregnant or planning to become pregnant
• you are breastfeeding
• you have epilepsy where you get mixed types of seizures (fits) which include absences
• you have any eye problems such as glaucoma (increased pressure in the eye)

Taking carbamazepine

How can carbamazepine be taken?

You can take carbamazepine as a tablet or as a liquid medicine.

Carbamazepine tablets are available in 100mg, 200mg and 400mg strengths.

There are two different types of tablets for carbamazepine:

• slow release (SR), prolonged release or modified release. These must not be chewed, or they will not give you the long-lasting effect. You should swallow each tablet whole or break it in half along the line in the middle
• ordinary tablets that should be swallowed whole or broken in half along the line in the middle

You should only take carbamazepine as agreed with your doctor

You will get the best effect from this medicine if you take it regularly without missing doses.

Make sure that you know your dose. If it is not written on the label, check it with your pharmacist or doctor.

You may have to take it more than once a day.

You will probably start on a low dose and it will increase until it is right for you.

It doesn’t matter what time you take it each day – choose a time that you can always remember. This could be a mealtime, or when you brush your teeth.

You can take it before or after food.

Different brands of carbamazepine tablets can release slightly different amounts of carbamazepine, even if they are the same strength. Ask your pharmacist to always give you the same brand of tablets. Keep the box or blister pack to show them. This is more important if you are taking carbamazepine for seizures (fits).

What if I miss a dose?

If you forget to take a dose, take it as soon as possible unless it is less than four to six hours until your next dose.

If you forget to take it by the time of the next dose, just take the next dose.

Do not take a double dose.

What will happen if I forget to take my carbamazepine?

If you forget to take your tablets for a few days, you may start getting your old symptoms back. Talk to your doctor if this happens.

You may need to restart the carbamazepine slowly or find a different treatment.

Stopping the use of carbamazepine

Once you start taking carbamazepine, the brain adjusts to the new balance of chemicals.

If you stop taking the carbamazepine all at once, the balance starts to change again. You could get your old symptoms back.

There is a risk that you may get seizures (fits). This is because even if you are not taking the carbamazepine for epilepsy, your body has got used to having an anticonvulsant medication on board.

When you decide with your doctor to stop taking carbamazepine, you will probably reduce the dose slowly over at least a month to stop you getting any uncomfortable withdrawal symptoms.

Go and speak to your doctor if you have missed a few doses or have decided to stop taking your medication.

The information on this page was reviewed by the College of Mental Health Pharmacy in October 2019.

Safety headlines

If you have taken more carbamazepine than the dosage recommended by the doctor who prescribed it to you, you must get medical help immediately – even if you do not feel any different.

While taking carbamazepine some people may think about hurting themselves or taking their own lives. You must go straight to hospital with your tablets if you have any of these thoughts.

If you get a rash just after starting to take carbamazepine, especially if you are from a Han Chinese or Thai family, you must stop the tablets and see a doctor straight away. You may get a fever, headache and body ache, like having flu, and then ulcers in your mouth and all over your body.

Carbamazepine may also cause other serious side effects: allergic reactions (difficulty breathing, swelling of your face or throat, itching skin lumps), and other serious symptoms that you can find here. Go to a hospital with your medicine if you get any of these symptoms.

Do not take carbamazepine if you have taken a monoamine oxidase inhibitor antidepressant (MAOI) like moclobemide, phenelzine, isocarboxazid or tranylcypromine in the last 14 days.

Carbamazepine can make the contraceptive pill or implant less effective – use a barrier method to stop you getting pregnant.

Stopping carbamazepine suddenly can cause serious side effects – go to your doctor if you want to stop, or if you are having these effects.

You might feel sleepy or dizzy in the first few days after taking carbamazepine – do not drive a car, ride a bike or operate machines until you see how this affects you.

Use good contraception while you are taking carbamazepine.

If you take carbamazepine while you are pregnant, it may affect the developing baby. It can also cause symptoms in newborn babies if you take it at the end of pregnancy. Talk to your doctor or midwife about this and get their help.

When to go to the hospital

If you have taken more carbamazepine than the dosage recommended by the doctor who prescribed it to you – even if you do not feel any different. Go to A&E. Take your medicine with you, to show to the doctors. Tell them how much you have taken. Get a friend or family member to go with you if you can, just in case you feel ill on the way.

You might get any of the following signs:

• feeling sleepy or confused
• slurring when you speak
• feeling agitated or sensing things that are not there
• unusual movements that you cannot control
• having seizures (fits)
• your breathing going very slow
• fast heartbeat, and a possible heart attack
• being sick
• blurred eyesight
• finding it hard to go for a wee

While taking carbamazepine, some people may think about hurting themselves or taking their own lives. This can happen to anyone, including people who are under 18. You must go straight to hospital if you have any of these thoughts. Take your tablets with you and tell the doctor that you are taking carbamazepine.

Stop taking carbamazepine and go to a doctor or hospital straight away if you get any of the following symptoms:

• serious skin reactions such as rash; red skin; blistering of the lips, eyes or mouth, or sex organs; or skin peeling with a fever (these reactions may be more frequent in patients of Chinese or Thai origin)
• mouth ulcers or unexplained bruising or bleeding
• sore throat or high temperature, or both
• jaundice (yellowing of your skin or the whites of your eyes)
• swollen ankles, feet or lower legs
• pain in your joints and muscles, a rash across the bridge of the nose and cheeks, and problems with your breathing (these may be the signs of a rare reaction known as systemic lupus erythematosus (SLE))
• fever, skin rash, joint pain, and unusual results of blood and liver function tests (these may be the signs of a multi-organ sensitivity problem)
• wheezing and coughing, difficulty breathing, feeling faint, rash, itching or facial swelling (these may be the signs of a severe allergic reaction)
• severe stomach pain

Side effects

Side effects that start when you begin taking carbamazepine should improve or go away after a few days or weeks. If they don’t, or they get worse, you should go back to your doctor.

Do not stop taking the tablets until you talk to your doctor, or you may get withdrawal symptoms as well.

Very common side effects of taking carbamazepine (affecting more than one in ten people) include:

• leucopoenia (a reduced number of the cells which fight infection making it easier to catch infections)
• dizziness and tiredness
• feeling unsteady or finding it difficult to control your movements
• feeling or being sick
• changes in liver enzyme levels (usually without any symptoms)
• skin reactions, which may be serious

Common side effects of taking carbamazepine (affecting up to one in ten people) include:  

• changes in the blood making you more likely to bruise or bleed
• fluid retention and swelling
• weight increase
• low sodium in the blood which might result in confusion
• headache
• double or blurred vision
• dry mouth
• loss of appetite

There are other side effects that you can get when taking this medicine – we have only included the most common ones here. Please look at the leaflet inside your medicine box, or ask a doctor or pharmacist, if you want to know if you are getting a side effect from your medicine.

When taking this medication, you are also at risk of developing a rare side effect called Steven-Johnson Syndrome. Symptoms are flu-like at first (fever, headache and all-over body ache) then ulcers could appear in your mouth, throat, nose and sex organs. You could also get conjunctivitis (red eyes) and a rash that spreads all over your body. If you think you are getting these symptoms, stop taking the tablets immediately and see a doctor without delay.

Body

Carbamazepine can cause weight gain or weight loss.

It is hard to know how it will affect each person until you take it.

Talk to your doctor about this if it worries you.

Sex and fertility

Sex

Carbamazepine can have side effects that might affect your sex life. These include:

• swelling of the breasts and some milk flow (regardless of gender)
  
• not wanting to have sex as much as usual, or at all
• spotting and/or bleeding between periods
  
• difficulty getting an erection (getting hard)

These effects should pass after the first couple of weeks. If they do not, and this is a problem for you, go back to the doctor and see what else you could try.

Fertility

There have been a few reports of lower sperm count and quality in people who are taking carbamazepine. Talk to your doctor about this if you are affected and trying to have a baby with your partner.

Carbamazepine can make hormone contraceptives like 'the Pill' and implants less effective – you might need to change your contraceptive to avoid the risk of pregnancy.

Condoms and other barrier methods (cap, diaphragm) will not be affected by carbamazepine so you can use those safely while taking it.

Pregnancy, post-natal and breastfeeding

Pregnancy

There have been reports of effects on the development of the baby from people who took carbamazepine during pregnancy. The risk is lower if your dose of carbamazepine is less than 1g (1000mg) per day.

If you become pregnant while taking carbamazepine, you should talk to your doctor about whether you should carry on taking it.

Your doctor should give you supplements like folic acid and vitamin K which are safe to take with carbamazepine.

Your dose of carbamazepine may need to increase later in pregnancy to keep the benefit.

Post-natal

Carbamazepine can cause some symptoms in some newborn babies like sleepiness, difficulty feeding, being sick and having diarrhoea (loose poo).

Your baby may need a vitamin K injection to help with healthy blood-clotting.

Some newborn babies have had seizures (fits) or breathing problems.

Your midwife can look out for this and give you help.

Breastfeeding

Some carbamazepine is passed to the baby in breast milk – you may breastfeed but look out for any side effects like heavy-sleeping or skin reactions.

Talk to your doctor or midwife about the risks and benefits of breastfeeding or ask to be referred to a lactation consultant.

Extra checks may be made on your baby for any liver problems or skin rashes.

Driving and transport

Do not drive a car or ride a bike just after you start taking carbamazepine.

Taking carbamazepine may make you feel sleepy or dizzy, and may affect your eyesight, when you start taking it.

This could affect you if you drive a car, ride a bike, or do anything else that needs a lot of focus. It might be best to stop doing these things for the first few days, until you know how it affects you.

Do not worry - most people do these things as normal while taking carbamazepine.

School and exams

Try not to take carbamazepine for the first time just before your exams.

You may feel dizzy, restless or confused when you first take carbamazepine, and it could affect your eyesight.

You should talk to your doctor about any future exams if you are starting carbamazepine.

You might decide together to delay starting it until you have done them.

If they are more than a week away, however, you might find that it is better to start carbamazepine to improve your motivation to study.

Do not worry - most people take exams as normal while taking carbamazepine.

Friends and family

You may want to let your family and friends know you are taking carbamazepine so they can support you and help you look out for side effects.

For guidance on this, check out our page on getting support with your medication.

Sport

Carbamazepine is not a banned substance in sport.

It could, however, affect your concentration and eyesight.

If you play sports that need a lot of focus, you might want to stop for a short while when you start taking carbamazepine, to see how it affects you.

Do not worry - most people play sports as normal while taking carbamazepine.

Alcohol and street drugs

Alcohol

You can continue to drink alcohol while taking carbamazepine but having the two together might make you very sleepy.

If you drink a lot of alcohol, however, it could increase the carbamazepine level in your body, and this could be dangerous.

So, during the first few days, it might be best to stop drinking alcohol until you see how the medicine affects you.

If you want to drink alcohol, remember that you might be sleepy and make sure you can get home safely.

Street drugs

Using both cannabis and carbamazepine at the same time might make you feel sleepier.

Cannabis and other drugs may have their own side effects on your mental health, like anxiety or psychosis. For more information, have a look at our drugs and alcohol page.

Carbamazepine reduces the level of methadone in the body when they are used together, so if you stop carbamazepine your methadone level might go up dangerously – talk to your doctor about this before you stop carbamazepine.

Carbamazepine drives cocaine breakdown to make norcocaine. This chemical is more dangerous to your heart and liver than cocaine itself.

Taking carbamazepine and alcohol together can affect your liver, so you may want to have regular liver function tests.

Prescription medicines

Many medicines, including some vitamins, do not mix well with carbamazepine and the dose of some medicines will need to be adjusted.

Talk to your doctor about any medications you are taking before you begin treatment with carbamazepine.

Talk to your pharmacist if you buy any medications over the counter to treat common illnesses like colds and flu or topical applications that you put on your skin.

Other interactions

Do not take carbamazepine tablets with grapefruit juice. Grapefruit juice may increase the absorption of carbamazepine from the gut and cause the levels of carbamazepine to increase.

Monitoring

When you start taking carbamazepine, the doctor should weigh you and do some blood tests to check your blood and liver function.

These weight and blood tests should be done again after every six months of taking carbamazepine.

A blood test might also be done every six months to check the levels of carbamazepine. If carbamazepine is helping improve your mood and you are not getting side effects, then levels are less important. Levels are more likely to be done if you are taking carbamazepine for seizures (fits) as there is a finer balance to be kept.

References and further reading

For more helpful links and information, have a look at our references and further reading page.