Phenobarbital

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Jul 07, 2022

Warnings

What are the risks of taking phenobarbital?

Phenobarbital is not safe for everyone. This seizure medication can cause serious health complications in some people. Talk to your healthcare provider or pharmacist if these risks are a concern.

Some of the risks of phenobarbital include:

DEPENDENCE: Phenobarbital can be habit-forming and may cause psychological and physical dependence if misused. You should take this medication exactly as prescribed by your doctor. The risk of physical dependence is higher in people who have a personal history or family history of drug abuse.
WITHDRAWAL SYMPTOMS: Stopping phenobarbital suddenly can lead to unpleasant withdrawal symptoms. If you have been taking phenobarbital for a while or taking this medication at high doses and wish to stop it, talk to your doctor about how to do so safely. Your doctor can advise you about coming off phenobarbital gradually so that you experience minimal withdrawal symptoms.
AGITATION OR EXCITEMENT: Phenobarbital can cause excessive excitement or agitation in some people. The risk is greater in children and older adults and those with extreme weakness or acute or chronic pain. Tell your doctor if you experience confusion, excitement, or agitation after taking phenobarbital.
EXTREME DROWSINESS: Phenobarbital can cause drowsiness, especially when you first start taking it. The drowsiness can be made worse if you drink alcohol or take other medicines that cause sedation. You should not drive or do anything that requires concentration until you know how phenobarbital affects you.
SLOWED BREATHING: If you experience weak or shallow breathing while on phenobarbital, seek medical attention immediately. The risk of slowed breathing is higher in people with severe liver disease.
BIRTH DEFECTS: Phenobarbital use during pregnancy can cause birth defects in the baby. Also, babies exposed to phenobarbital during the third trimester of pregnancy can experience withdrawal symptoms after birth. Tell your doctor if you are pregnant before starting phenobarbital. Call your doctor immediately if you become pregnant while taking this seizure medication.

If you are at a high risk of complications from phenobarbital use, your doctor or pharmacist can help you find other treatments for your condition.

What should I tell my doctor before taking phenobarbital?

Tell your doctor if you are allergic to phenobarbital or any ingredients in the tablets or elixir. Your pharmacy can provide you with a list of ingredients. Also, tell your doctor if you have an allergy to any other barbiturates such as amobarbital (Amytal), butabarbital (Butisol), secobarbital (Seconal), pentobarbital, or any other medications.

Give your doctor and pharmacist a complete list of your current medicines, including prescription and over-the-counter medications, vitamins, and herbal products. This can help avoid serious drug interactions.

Give your doctor a complete medical history, especially if you have ever had liver disease, kidney disease, adrenal gland disease, breathing problems, or a condition called porphyria. Also, tell your doctor if you suffer from acute or chronic pain, depression, or have ever had thoughts of harming or killing yourself.

Tell your doctor if you have a history of drug abuse (street drugs or prescription drugs) or if you have ever consumed large amounts of alcohol.

Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. Phenobarbital can be harmful to the baby if you take it during pregnancy. If you are breastfeeding, phenobarbital can pass into breast milk. If your doctor decides to treat you with phenobarbital while breastfeeding, you will need to watch your baby for drowsiness or poor growth signs.

If you are over 65 years of age, discuss the risks versus benefits of taking phenobarbital with your doctor. There may be other safer medications available to treat your condition.

Tell your healthcare providers you are on phenobarbital before undergoing surgery, including dental surgery.

You should be aware that because of its pharmacokinetics, phenobarbital can make hormonal contraceptives less effective because of its pharmacokinetics. This includes oral contraceptives (birth control pills), patches, implants, rings, injections, and intrauterine devices. Patients treated with phenobarbital should get their doctor’s advice about appropriate birth control methods.

What precautions should I take while taking phenobarbital?

Keep all your appointments at your doctor’s office. Your doctor may order lab tests to check phenobarbital blood levels and adjust your dose.

Make a list of all your medications and take it to every healthcare appointment.

Tell your doctor if you miss your period or become pregnant while taking phenobarbital.

Phenobarbital can make you drowsy and dizzy. Do not drive or do anything that requires focus until you know how it affects you. You should know that drinking alcohol can worsen the drowsiness caused by phenobarbital.

What are phenobarbital interactions?

Taking phenobarbital with certain other drugs can affect how the medication works or increase the risk of severe side effects. Your doctor may choose a different medication, change the dose or frequency of your medicines, and/or monitor you carefully for side effects if there are known drug interactions.

There can be drug interactions between phenobarbital and the following medications:

Blood thinners (anticoagulants) such as warfarin (Coumadin)
Antibiotics like doxycycline (Vibramycin)
Antifungal medications like griseofulvin (Fulvicin)
Sleeping pills, sedatives, and tranquilizers

Disulfiram (Antabuse) - a medicine used to treat chronic alcoholism
Hormone replacement therapy (HRT)
Monoamine oxidase inhibitors (MAOIs) such as phenelzine (Nardil), isocarboxazid (Marplan), tranylcypromine (Parnate), and selegiline (Eldepryl, Emsam, Zelapar)

Medications used to treat anxiety, depression, allergies, colds, pain, or asthma
Certain other seizure medications like valproic acid (Depakene) and phenytoin (Dilantin)
Steroids like methylprednisolone (Medrol), dexamethasone (Decadron, Dexone), and prednisone (Deltasone)

All possible drug interactions of phenobarbital are not included in this list. Give your healthcare provider a complete list of your medications, including prescription drugs, over-the-counter medicines, dietary supplements, vitamins, and herbal remedies. Also, tell your healthcare provider if you smoke, drink alcohol, or use illegal drugs because some of these substances can cause serious health complications when used with prescription drugs.

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