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Phenobarbital for Epilepsy


Generic NameBrand Name

Primidone is a drug that the body converts into phenobarbital.

How It Works

Phenobarbital is a barbiturate, which acts as a sedative or depressant.

Why It Is Used

Phenobarbital is the antiepileptic drug of choice for newborns who have epilepsy.

Partial seizures and generalized tonic-clonic seizures may be treated with phenobarbital.

How Well It Works

Phenobarbital is often effective in controlling partial and generalized tonic-clonic seizures.1

Side Effects

Phenobarbital often makes children and older people:

  • Hyperactive.
  • Restless.
  • Unable to sleep.
  • Aggressive.

Phenobarbital has the opposite effect on young and middle-aged adults, who may feel:

  • Listless.
  • Depressed.
  • Tired.

Phenobarbital can alter your mood, behavior, thought processes, and ability to learn or remember things. These effects may be worse in older people.

Using phenobarbital for a long time can increase your risk for osteoporosis and broken bones.

FDA Advisory. The U.S. Food and Drug Administration (FDA) has issued an advisory on antiepileptic drugs (AEDs) and the risk of suicide. Talk to your doctor about these possible side effects and the warning signs of suicide in adults and in children and teens.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

It may take time and careful, controlled adjustments by you and your doctor to find the combination, schedule, and dosing of medicine to best manage your epilepsy. The goal is to prevent seizures while causing as few side effects as possible. After you and your doctor figure out the medicine program that works best for you, make sure to follow your program exactly as prescribed.

  • Adverse effects. Phenobarbital's effect on your thinking and state of mind is a serious drawback to using the drug. Teenagers and adults taking the drug may feel depressed or irritable. It can cause memory loss and decrease your ability to learn. Children and older adults may feel restless and have trouble sleeping. Primidone is usually less effective and has more side effects than phenobarbital (including depression and impotence).
  • Drug interactions. Many medicines for epilepsy can interact with other medicines you may be taking. This means that your epilepsy medicine may not work as well, or it may affect the way another medicine you are taking works. Some of these interactions can be dangerous. Make sure to tell your doctor about all the medicines, herbal pills, and dietary supplements you are taking. Phenobarbital may reduce the effectiveness of birth control pills. A woman taking phenobarbital may need to use a method of birth control other than birth control pills to reduce her chances of becoming pregnant.
  • Risk of birth defects. All medicines for epilepsy have some risk of birth defects. But the risk of birth defects needs to be carefully compared to other risks to the baby if the mother stops taking her epilepsy medicine. If you are thinking about becoming pregnant, be sure to plan ahead and talk with your doctor about the benefits and risks of taking epilepsy medicine during your pregnancy. It you are already pregnant, it is not too late. The best thing to do is talk to your doctor about your pregnancy before you make any changes to the medicines you are taking.
  • Ease of use. Phenobarbital only has to be taken once a day, making it a good choice if you have a busy schedule or have trouble remembering to take your medicine. Because phenobarbital works very slowly, it may take weeks before phenobarbital levels reach the proper level. But missing a dose of phenobarbital now and then usually does not affect the drug levels in your bloodstream. This is not true of other antiepileptic drugs.
  • Other concerns. For some people, phenobarbital may cause side effects or carry risks that are not yet fully known. Report any unexpected side effects or problems to your doctor.

Complete the new medication information form (PDF) (What is a PDF document?) to help you understand this medication.



  1. Drugs for epilepsy (2008). Treatment Guidelines From The Medical Letter, 6(70): 37–46.


By Healthwise Staff
John Pope, MD - Pediatrics
Steven C. Schachter, MD - Neurology
Last Revised August 28, 2013

Last Revised: August 28, 2013

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