Phenobarbital is available in Canada by prescription only.

Known as



Phenobarbital (the longest-established anticonvulsant medication) controls epileptic seizures, depresses the central nervous system and is used occasionally as a sedative. It is generally used to control tonic-clonic, and simple partial seizures. There is disagreement about its efficacy for complex partial seizures.

How to Use

Phenobarbital can be taken orally or by rectal suppository. It is usually given with other anti-epileptic medications.

Side Effects

Common reactions may include drowsiness, headache, depression, insomnia, elation, confusion, breathing difficulty, high blood pressure, skin rash and other allergic reactions, and an increased risk of liver disease.


Long-term use of phenobarbital may result in addiction. Abrupt withdrawal may cause nightmares, forgetfulness, irritability, weight loss, and convulsions. Alcohol should be avoided. Patients with liver disease, a history of drug dependence, respiratory problems, high blood pressure and pains in the limbs should inform their doctor if these problems occur while using phenobarbital. Because phenobarbital may impair physical and mental abilities, do not operate vehicle or other hazardous machinery while taking it. Women should report pregnancy to their physicians promptly.


  • Phenobarbitol may increase the action of acetaminophen (Tylenol).
  • Phenobarbital may decrease the action of oral contraceptives and verapamil.
  • Antihistamines, corticosteroids, narcotic pain killers, tranquilizers, phenytoin and valproic acid may increase the action of phenobarbital.
  • The therapeutic effect of phenobarbital may increase or decrease when taken with other anticonvulsants.
  • If you are using any other drug or are pregnant (first trimester), inform your doctor.

New Moms: If the newborn baby of a mother who took barbiturates while pregnant shows a pattern of being irritable and vomits repeatedly, don’t be alarmed: the infant is experiencing withdrawal symptoms. Also mothers who breastfeed should note if the baby is drowsy, resistant to feeding or has skin rash. If so, discontinue breastfeeding.

Missed Dose

Take next dose as soon as you remember, then resume medication as usual. Do not double the dosage to catch up on therapeutic effect.


Store at room temperature between 15°C and 30°C. Keep away from children, heat, light and moisture.


  • Tablets: 15, 30 to 600 mg.
  • Ampoules for injection.
  • Other barbiturates are administered by injection in hospital. Dosages vary according to therapeutic effect required.

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DisclaimerExpand Disclaimer Section

The material offered at this site is to provide general information about epilepsy to the public. It is not intended to be taken as medical advice. Although all material presented at this site has been thoroughly researched and is believed to be correct, Epilepsy Ontario accepts no liability. Consult your physician and/or neurologist with any questions you have. People with epilepsy should never discontinue anti-epileptic medications or make changes in activities unless specifically advised to do so by an attending physician.