Phenobarbital (FEE noe BAR bi tal) is used as an anticonvulsant. This labeling has not been approved by the FDA and it has not been found by the FDA to be safe and effective.

Your epilepsy treatment should always be discussed with your healthcare provider before use. Based on their judgment and knowledge, a drug may be prescribed for other epilepsy types not included in the indications. For more information, please see the prescribing information.

How can you take phenobarbital? (Available formulations)

Phenobarbital is available as a tablet, injection solution, or oral solution.

Who should not take phenobarbital?

If you are allergic to phenobarbital, barbiturates, or any of the inactive ingredients, then you should not take it. If you have a personal or familial history of acute intermittent porphyria should not take phenobarbital. If you have marked impairment of liver function, respiratory disease in which shortness of breath or obstruction is evident, or have known previous addiction to the sedative/hypnotic drugs, then you should not take phenobarbital.

Other considerations may influence whether you should take phenobarbital. Tell your healthcare provider if you:

  • have or have had depression, mood problems, or suicidal thoughts or behavior.
  • have borderline hypoadrenal function (underactive adrenal gland).
  • have liver problems.
  • have abused or been dependent on prescription medicines, street drugs, or alcohol.
  • are pregnant or plan to become pregnant.
  • are breastfeeding or plan to breastfeed.

What is important to know about taking phenobarbital?

Do not stop taking phenobarbital suddenly unless directed to do so by your healthcare provider.

As with all antiseizure medications, phenobarbital should be withdrawn gradually to minimize the risk of causing or worsening seizures or status epilepticus. You should not stop using phenobarbital suddenly unless your healthcare provider tells you to stop the medicine because of a serious side effect.

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.

Taking phenobarbital with certain other medicines may cause side effects or affect how well they work. Do not start or stop other medicines without talking to your healthcare provider. Especially tell your healthcare provider if you take: coumarin anticoagulants.

Women or those who are/plan to become pregnant
Use in pregnancy

At this time, there is not enough evidence regarding developmental risks associated with the use of phenobarbital in pregnant people. In animal studies, there were instances of developmental issues at clinically relevant doses. However, having a seizure during pregnancy could harm both the pregnant individual and the baby. Tell your healthcare provider right away if you become pregnant. Do not start or stop taking seizure medication during pregnancy without your healthcare provider’s advice.

If you become pregnant while taking phenobarbital, talk to your healthcare provider about registering with the North American Antiepileptic Drug (NAAED) Pregnancy Registry. The purpose of this registry is to collect information about the safety of antiseizure medicine during pregnancy. You can enroll in this registry by calling 1-888-233-2334.

Use during breastfeeding

It is unknown if there are effects on the breastfed infant, or if phenobarbital impacts milk production. Talk to your healthcare provider about the risks. Your healthcare provider will consider the developmental and health benefits of breastfeeding along with your need for phenobarbital and the potential effect on the infant from phenobarbital or from your epilepsy.

Effect on birth control and fertility

Phenobarbital may decrease the effectiveness of hormonal contraceptives, including birth control pills, injections, implants, skin patches, and vaginal rings. To prevent pregnancy while using phenobarbital, use a barrier form of birth control: condom, diaphragm, cervical cap, or contraceptive sponge.

What are the side effects of phenobarbital?

Phenobarbital is not approved by the FDA. There are risks associated with all medicines. Some side effects caused by phenobarbital can be very serious, and even life-threatening. It is important to be informed about these serious reactions and to be aware of their symptoms.

Common side effects

The most common side effects that were reported in studies of phenobarbital are central nervous system depression, respiratory depression, apnea (temporarily stopped breathing during sleep), circulatory collapse, hypersensitivities, nausea and vomiting, headache.

Rare, but serious side effects

Abuse, misuse, and addiction

Phenobarbital is a federally controlled substance (Schedule IV) as it has a risk of abuse, misuse, and addiction, which can lead to overdose or death. Using phenobarbital more frequently than recommended, even at recommended dosages, may increase these risks, especially when used in combination with other medications (e.g., opioids), alcohol, and/or illicit substances. Talk to your healthcare provider about the signs and symptoms of phenobarbital addiction.


In small doses, the barbiturates may increase the reaction to painful stimuli. Taken by themselves, the barbiturates cannot be relied upon to relieve pain or even to produce sedation or sleep in the presence of severe pain.