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Phenobarbital

Anticonvulsant Sedative

Brand names:

Sezaby®

Other names:

Phenobarbital sodium, Luminal sodium, Phenobarbitone, Phenylethylmalonylurea

Often used for:

Seizures, sedation for procedures

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What is phenobarbital?

Phenobarbital is a medicine used to treat seizures and for sedation during procedures. It works by slowing the activity of the brain.

Phenobarbital can also be used to reduce anxiety, manage opioid withdrawal in newborn babies, or for high levels of bilirubin in the blood.

This medicine may be given in the clinic, hospital, or at home. 

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May be given as a tablet by mouth

 
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May be given as a liquid by mouth

 
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May be given as a shot into a muscle (intramuscular injection)

 
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May be given into a vein by IV

 
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Possible side effects

  • Low blood pressure
  • Increased excitement, agitation, and hyperactivity
  • Feeling depressed
  • Shortness of breath or slower than normal rate of breathing
  • Feeling tired or weak
  • Nausea and vomiting
  • Loss of appetite, especially in neonates
  • Headache
  • Constipation
  • Dizziness
  • Confusion
  • Trouble sleeping, nightmares
  • Slow (low) heart rate
  • Temporary changes in liver function

Call your care team right away if your child has symptoms of an allergic reaction. These may include: rash, hives, itching, runny nose, fever, chills, headache, muscle ache, shortness of breath, coughing, tightness in the throat, swelling of the face or neck, dizziness, low blood pressure, or pain in the chest, side, or back.  

Not all patients who take phenobarbital will have these side effects. Common side effects are in bold, but there may be others. Report any symptoms or side effects to your health care provider or pharmacist.

Find more information on side effects.

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Tips for patients and families

Be sure to discuss all questions and instructions with your health care provider or pharmacist. 

  • Many medicines interact with phenobarbital, which may result in a medication not working or more side effects. Some of these include warfarin, cyclosporine, theophylline, steroids, birth control pills, other seizure medicines, griseofulvin and doxycycline. Tell your care provider and pharmacist about all medicines your child takes. 
  • This medicine may be habit-forming with long-term use. Let your care team know if you are concerned about this happening. 
  • Your care team may draw levels of the medicine in the blood. Follow all instructions on how these tests will be performed.
  • This medicine may make your child dizzy or drowsy. Do not let your child do anything that could be dangerous, such as drive or ride a bike, until you see how this medicine affects them.
  • Watch for changes in your child’s mood or mental health, such as worsening depression, anxiety, agitation, irritability, panic attacks, and trouble sleeping.
  • Stopping this medicine too fast can result in unwanted side effects. Your care team will monitor and plan if the medicine must be stopped.     
  • It is important that patients tell the care team if they are sexually active, pregnant, or breastfeeding. 
  • This medicine may make birth control pills and other hormone-based birth control methods less effective. Sexually active patients should use another form of birth control, like condoms, to prevent pregnancy while taking this medicine.

Phenobarbital at home

  • This medicine can be taken with or without food. Take with food if stomach upset occurs. 
  • Tablets: Take as directed. Swallow tablets whole unless otherwise instructed. 
  • Liquid bottled medicine: Shake well. Use the measuring device that comes with the medicine. You may mix the medicine with chocolate syrup right before giving it to improve the taste.
  • It is important to take phenobarbital exactly as your care team instructed. This will keep the blood levels constant during the day and night. 
  • In case of a missed dose, if the next dose is not due for at least 4 hours, give the missed dose as soon as possible. If the next dose is due in less than 4 hours, skip the missed dose. Do not give 2 doses at the same time. 
  • Store at room temperature in a dry place. Do not store in a bathroom.

Learn more about phenobarbital

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Always check the medication label. Many medicines look the same. Do not take any new medicine, including over-the counter medicines or supplements, without checking with your doctor or pharmacist. Talk to your doctor or pharmacist about what to do in the case of a missed dose, allergic reaction, or medical emergency. 

This information is not intended to be a complete guide and is not a substitute for talking with your provider. Medicine names, appearance, formulas, or availability may vary by clinic location. Always follow the instructions given by your care team.

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Reviewed: October 2025