ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.
Overview
It's a controlled substance.
What it's used for
- Seizures
- Newborn seizures
- Off-label: alcohol withdrawal
How to take it
- Take it at the same time each day.
- Don't stop suddenly.
Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.
Side effects
Common side effects
- Sleepiness
- Dizziness
- Behavior changes in children
Call 911Slow, shallow, or stopped breathing, blue lips, or can't be woken up
Call 911A blistering, peeling, or widespread red rash, especially with fever
Call 911Thoughts of suicide or harming yourself. Call or text 988 any time.
Warnings
- It makes hormonal birth control less effective.
Other medicines, foods, and alcohol
- Alcohol, opioids, and sedatives can dangerously slow breathing.
- It lowers levels of many medicines, including warfarin.
Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.
Pregnancy and breastfeeding
Talk with your provider before pregnancy.
Missed doses, overdose, and storage
If you miss a dose
Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.
If someone takes too much
Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.
Storing it
Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.
Conditions it's used for
Sources
- DailyMed: FDA drug label for Phenobarbital (U.S. National Library of Medicine)
- MedlinePlus: Drugs, herbs, and supplements
- FDA: Drugs@FDA
Last updated 2026-11-13.