Jul 28, 2022

Generic name: phenobarbital [ FEE-noe-BAR-bi-tal ]
Brand names: Solfoton, Luminal
Dosage forms: oral elixir (20 mg/5 mL); oral tablet (100 mg; 15 mg; 16.2 mg; 30 mg; 32.4 mg; 60 mg; 64.8 mg; 97.2 mg)
Drug classes:  Barbiturate anticonvulsants ,  Barbiturates

What is phenobarbital?

Phenobarbital is a barbiturate (bar-BIT-chur-ate). Phenobarbital slows the activity of your brain and nervous system.

Phenobarbital is used to treat or prevent  seizures . Phenobarbital is also used short-term as a sedative to help you relax.

Phenobarbital may also be used for purposes not listed in this medication guide.


You should not use phenobarbital if you have severe  liver disease , severe  asthma  or  COPD , a personal or family history of  porphyria , or a history of addiction to drugs similar to phenobarbital.

Before taking this medicine

You should not take phenobarbital if you are allergic to phenobarbital or other  barbiturates  (Nembutal,  Seconal , and others), or if you have:

  • severe asthma, chronic obstructive pulmonary disorder (COPD), or other breathing disorder;
  • a personal or family history of porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
  • severe liver disease; or
  • a history of addiction to phenobarbital or similar medicines ( Valium ,  Xanax ,  Ativan , and others).

To make sure phenobarbital is safe for you, tell your doctor if you have:

  • liver disease;
  • temporary or  chronic pain ;
  • a pituitary gland disorder;
  • pheochromocytoma  (tumor of the adrenal gland);
  • kidney disease;
  • a food or drug allergy;
  • a condition for which you take a blood thinner ( warfarin ,  Coumadin ,  Jantoven ).

Follow your doctor’s instructions about taking seizure medication if you are pregnant. Seizure control is very important during pregnancy, and having a seizure could harm both mother and baby. Do not start or stop taking this medicine without your doctor’s advice, and tell your doctor right away if you become pregnant.

Phenobarbital can make  birth control pills  less effective. Ask your doctor about using a non-hormonal  birth control  (condom,  diaphragm  with  spermicide ) to prevent pregnancy.

It is not known whether phenobarbital passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

How should I take phenobarbital?

Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Phenobarbital may be habit-forming. Never share phenobarbital with another person, especially someone with a history of drug abuse or addiction. Keep the medication in a place where others cannot get to it. Selling or giving away this medicine is against the law.

Do not change your phenobarbital dose without your doctor’s advice. Tell your doctor if the medicine does not seem to work as well in treating your condition.

If you are taking phenobarbital to treat seizures, keep taking the medicine even if you feel fine.

Do not stop using suddenly after long-term use, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using phenobarbital.

Store at room temperature away from moisture, heat, and light.

Keep track of the amount of medicine used from each new bottle. Phenobarbital is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

Detailed Phenobarbital dosage information

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenobarbital can be fatal.

Overdose symptoms may include slow or shallow breathing, weak pulse, cold or clammy skin, little or no urination, pinpoint pupils, feeling cold, or fainting.

What should I avoid while taking phenobarbital?

Drinking alcohol with phenobarbital can cause side effects.

This medication may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Phenobarbital side effects

Phenobarbital may cause a severe allergic reaction. Stop taking phenobarbital and get emergency medical help if you have signs of an allergic reaction:  hives ; difficult breathing; swelling of your face, eyes, lips, tongue, or throat.

Phenobarbital may cause serious side effects. Call your doctor at once if you have:

  • weak or shallow breathing;
  • unusual pain anywhere in your body (especially in the neck, shoulder, or arms);
  • a red blood cell disorder–pale skin, muscle weakness,  diarrhea ,  weight loss , rapid heart rate, tongue swelling,  numbness  or tingling in your hands or feet, feeling short of breath; or
  • severe skin reaction–fever,  sore throat , swelling in your face or tongue, burning in your eyes, skin pain followed by a red or purple  skin rash  that spreads (especially in the face or upper body) and causes blistering and peeling.

Side effects such as confusion,  depression , or excitement may be more likely in older adults and those who are ill or debilitated.

Common side effects of phenobarbital may include:

  • drowsiness, lack of energy;
  • dizziness  or spinning sensation;
  • depressed mood;
  • feeling restless or excited (especially in children or older adults);
  • drunk feeling; or
  • “hangover” effect (drowsiness the day after taking phenobarbital).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Phenobarbital side effects  (more detail)

What other drugs will affect phenobarbital?

Taking phenobarbital with other drugs that make you sleepy or slow your breathing can cause dangerous or life-threatening side effects. Ask your doctor before taking phenobarbital with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for  anxiety , depression, or seizures.

Other drugs may interact with phenobarbital, including prescription and over-the-counter medicines,  vitamins , and  herbal products . Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.

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