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Phenobarbital for epilepsy

You need to take phenobarbital regularly every day. Take your dose at bedtime.

Phenobarbital may cause you to feel drowsy and unsteady. This often settles down as your body adjusts to the new medicine.

Do not drink alcohol.

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About phenobarbital

Type of medicine

An anti-epileptic medicine

Used for


Available as

Tablets, oral liquid and injection

If you have epilepsy, it means that you have had more than one unexplained fit, or seizure. A seizure is a short episode of symptoms caused by a burst of abnormal electrical activity in your brain. Different parts of the brain control different functions of your body, so the symptoms that occur during a seizure will depend on where the abnormal burst of electrical activity occurs. Symptoms that may occur during a seizure can affect your muscles, sensations, behaviour, emotions, consciousness, or a combination of these. The seizures can be prevented in most people by suitable anti-epileptic medication.

Phenobarbital works by stabilising the electrical activity of your brain, which helps to prevent the seizures from occurring.

Before taking phenobarbital

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking phenobarbital it is important that your doctor knows:

  • If you are pregnant, trying for a baby or breastfeeding.

  • If you have breathing problems.

  • If you have ever had problems with drug or alcohol dependence.

  • If you have any problems with the way your kidneys work, or with the way your liver works.

  • If you have a rare inherited blood disorder called porphyria.

  • If you are taking any other medicines. This includes any medicines 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.

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How to take phenobarbital

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about phenobarbital and will provide you with a full list of the side-effects which you may experience from taking it.

  • Take phenobarbital exactly as your doctor tells you to. It is usual to take one dose a day, at bedtime. Your doctor will tell you how many tablets to take for the dose. This information will also be printed on the label of the pack to remind you about what the doctor said to you. You need to take phenobarbital regularly every day to prevent the fits (seizures) from occurring.

  • Try to take your doses of phenobarbital at the same time each evening. Having a routine like this will help you to remember to take your doses regularly. Swallow the phenobarbital tablets with a drink of water. You can take them either with or without food.

  • If you forget to take a dose, take it as soon as you remember unless it is nearly time for your next dose, in which case leave out the missed dose. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress. You may need to have blood tests from time to time.

  • When you first start a new treatment for epilepsy there may be a change in the number or type of fits (seizures) you experience. Your doctor will advise you about this.

  • Phenobarbital made by different manufacturers can act in a slightly different way in your body. Because of this, it is recommended that you continue to take tablets/medicine from the same manufacturer as you have had before. So, each time you collect a prescription, check to make sure your supply looks the same. If you are unsure, or if have any questions about your prescription, please ask your pharmacist to check it for you.

  • While you are being treated for epilepsy there is a small risk that you may develop mood changes, distressing thoughts and feelings about suicide. If this happens, you must tell your doctor about it straightaway.

  • People with epilepsy must stop driving at first. Your doctor will advise you about when it may be possible for you to resume driving again. This will usually be after a year free of seizures.

  • Do not stop taking this medicine unless your doctor tells you to do so. Stopping it suddenly can cause your seizures to return and your doctor will want you to reduce your dose gradually if this becomes necessary. Also, taking phenobarbital over a time can lead to your body becoming dependent on it and this is another reason why your doctor will want to reduce your dose slowly.

  • You are advised not to drink alcohol while you are taking phenobarbital. Phenobarbital will make you feel sleepy and drinking alcohol will increase this.

  • If you are due to have an operation or any dental treatment, please tell the person carrying out the treatment that you are taking phenobarbital.

  • If you buy any medicines, check with a pharmacist that they are suitable for you to take alongside phenobarbital.

  • You should avoid becoming pregnant while you are taking phenobarbital because it could cause harm to your unborn baby.

  • If you are a woman using hormonal contraception ('the pill' or the 'mini pill'), discuss this with your doctor, as phenobarbital interferes with these and could mean you are more likely to become pregnant. Other methods of contraception will be more suitable for you.

  • If you want to have a family, make sure you discuss this with your doctor well in advance of becoming pregnant. This is so that you can be given advice from a specialist before you become pregnant. If you become pregnant while you are taking phenobarbital, you should tell your doctor straightaway.

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Can phenobarbital 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 most common ones associated with phenobarbital. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.


phenobarbital side-effects

What can I do if I experience this?

Feeling unsteady

Getting up or moving more slowly should help. If this continues, let your doctor know

Feeling sleepy or tired

Make sure your reactions are normal before you use tools or machines

Feeling short of breath, behavioural changes, mood changes (such as feeling irritable, confused, excited or depressed), impaired memory

If any of these become troublesome, speak with your doctor

Important: your doctor will have discussed with you the possibility of some less common but more serious side-effects. Let your doctor know straightaway if you experience any of the following:

  • A high temperature (fever) and swollen glands.

  • A severe skin rash.

  • Yellowing of your skin or the whites of your eyes (jaundice).

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

How to store phenobarbital

  • 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

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 at once. 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.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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