Phenobarbital Overdose: Signs, treatment and who’s at risk
The signs of a phenobarbital overdose, why mixing it with alcohol or opioids is so dangerous, what hospitals do, what to do for pets, and how its status differs in five countries.
A phenobarbital overdose is a medical emergency. Too much of this long-acting seizure medicine slows the brain and breathing, and can cause deep sleepiness, slurred speech, confusion, slow breathing, low body temperature, low blood pressure and coma. Mixing it with alcohol, opioids or benzodiazepines raises the danger. Call emergency services or poison control now, even if the person seems fine.
At a glance
- Phenobarbital has been on the World Health Organization’s Model List of Essential Medicines since 1977 as a medicine for epilepsy and seizures.
- With proper treatment, people can recover from a phenobarbital overdose in about 1 to 5 days, but a long coma, breathing problems or shock may cause permanent disability, according to MedlinePlus.
- There is no specific antidote for barbiturates, so hospitals support breathing and blood pressure while the body clears the drug.
- All five US phenobarbital tablet labels we checked on DailyMed in October 2026 are listed as “unapproved drug other” and carry the DEA Schedule IV (C-IV) mark.
- The FDA approved Sezaby, a phenobarbital injection for newborn seizures, on November 17, 2022, and conditionally approved Fidoquel-CA1 tablets for dogs with epilepsy on September 6, 2023.
What is phenobarbital?
Phenobarbital (called phenobarbitone in Australia and India) is a barbiturate, an older type of sedative. US labels list it as a sedative and as an anticonvulsant “for the treatment of generalized and partial seizures.” It comes as tablets, an oral liquid and injections.
Hospitals use it too. StatPearls notes it is recommended for status epilepticus (seizures that don’t stop) and is also used to treat alcohol and benzodiazepine withdrawal. Vets also prescribe it for dogs and cats with epilepsy.
What are the symptoms of a phenobarbital overdose?
Phenobarbital slows down the central nervous system, and an overdose slows it too far. Signs listed by MedlinePlus and US product labels include:
- Deep drowsiness, confusion, dizziness, fainting, or not waking up (coma)
- Slurred speech, weakness and a staggering walk, which MedlinePlus says is more common in children
- Slow or stopped breathing
- Very low blood pressure (shock) and low body temperature
- Blurred or double vision and fast, jerky side-to-side eye movements (nystagmus)
- Nausea and rash
- Blisters or sores where the body pressed against a hard surface during a long period of unconsciousness
Because phenobarbital is long-acting, these effects can last for days (see the questions below). For a checklist that covers other drugs too, see signs of an overdose.
What should you do if someone took too much phenobarbital?
- Call emergency services right away if the person is hard to wake, is breathing slowly or not at all, or has a seizure.
- Otherwise, call poison control now, even if they seem fine, including for an extra dose or a child who swallowed a tablet.
- If opioids might also be involved, give naloxone (Narcan) if you have it. See how to use naloxone.
- Don’t make them vomit, and don’t give food, drinks or other medicines unless a professional tells you to.
- Stay with them and don’t leave them to sleep it off. If they are breathing, turn them on their side (the recovery position). If they stop breathing, start rescue breathing or CPR if you are trained.
If you can, have the person’s age and weight, the product name, and when it was taken ready, but don’t delay the call to find them. Bring the container to the hospital.
Why is phenobarbital more dangerous with alcohol, opioids or benzodiazepines?
Each of these slows breathing and brain activity, and together the effects add up. US labels say “alcohol should not be consumed while taking barbiturates,” and that other sedatives, sleep medicines, antihistamines, tranquilizers and alcohol “may produce additive depressant effects.” StatPearls warns that combining barbiturates with benzodiazepines or opioids can cause oversedation and severe breathing problems.
Read more about alcohol overdose, benzodiazepines and opioid overdose. If you take phenobarbital, ask your pharmacist to check every new medicine, including over-the-counter sleep aids.
Is there an antidote for a phenobarbital overdose?
No. “No specific antidote exists for barbiturates,” says StatPearls. Naloxone (Narcan) reverses opioid overdoses, but phenobarbital is not an opioid, so naloxone will not undo its effects. Many overdoses involve more than one drug, though, so if opioids could be part of the picture, give naloxone while you wait for help.
How is a phenobarbital overdose treated in the hospital?
Care focuses on keeping the person breathing and their blood pressure stable until the body clears the drug. It can include:
- Oxygen, a breathing tube and a breathing machine (ventilator)
- IV fluids and, if needed, medicines that raise blood pressure
- Activated charcoal, which can reduce how much drug the gut absorbs
- Making the urine less acidic, which the label says speeds up how fast phenobarbital leaves the body
- Dialysis or hemoperfusion (machines that clean the blood) in serious cases
- Blood and urine tests, an ECG, a chest X-ray or a CT scan
An overdose is not a quiet sleep. Lying unconscious for a long time can cause blisters and sores, and a long coma, breathing complications or shock may cause permanent disability. Recovery depends on how quickly treatment starts, so get help early. Read more in what is an overdose.
Can stopping phenobarbital suddenly be dangerous?
Yes. US labels warn that dependence “may occur with continued use,” and that stopping suddenly after long use can cause withdrawal symptoms “including delirium, convulsions, and possibly death.” Don’t stop, skip or change your dose without talking to your prescriber, and contact your pharmacy early if you are running out.
Who is most at risk of a phenobarbital overdose?
- People who mix it with alcohol, opioids, benzodiazepines or other sedatives.
- Children who find tablets or liquid at home. Keep phenobarbital locked away.
- Homes with pets on phenobarbital, where human and pet tablets can get mixed up. Store them apart, in labeled containers.
Get rid of leftovers safely: see how to dispose of unused medicines.
What if a dog or cat gets too much phenobarbital?
The FDA notes that human phenobarbital tablets “have historically been used in veterinary medicine,” and in 2023 it conditionally approved Fidoquel-CA1 for dogs with epilepsy. A 2026 study in Frontiers in Veterinary Science calls it “widely regarded as a first-line treatment for feline epilepsy.”
If your pet got an extra dose or ate someone else’s tablets, call your veterinarian or an animal poison line right away, before signs such as wobbling or deep sleep appear:
- ASPCA Animal Poison Control Center: (888) 426-4435, open 24 hours a day. A consultation fee may apply.
- Pet Poison Helpline: (855) 764-7661, open 24/7. It charges an $89 (USD) fee per incident, including follow-up calls (as of October 2026).
If a person takes a pet’s phenobarbital by mistake, it is the same medicine. Call poison control.
Our analysis: phenobarbital’s unusual status in the US
Every US phenobarbital tablet label we opened says the product is not FDA-approved: “This drug has not been found by FDA to be safe and effective, and this labeling has not been approved by FDA.” The tablets are still prescription-only and controlled under DEA Schedule IV.
The tablets are also hard to tell apart. All the ones we checked are white and round, and makers use two strength systems: metric (15, 30, 60 and 100 mg) and old “grain” strengths (16.2, 32.4, 64.8 and 97.2 mg, equal to 1/4, 1/2, 1 and 1 1/2 grain). The imprint is often the only clue.
| Labeler | Strengths (mg) | Imprints | FDA marketing category |
|---|---|---|---|
| Par Health USA | 16.2, 32.4, 64.8, 97.2 | “V” with 5011, 5012, 5013, 5014 | Unapproved drug other |
| Trigen Laboratories | 15, 30, 60, 100 | 315, 330, 360, 310 | Unapproved drug other |
| Westminster Pharmaceuticals | 15, 16.2, 30, 32.4, 60, 64.8, 97.2, 100 | 1, 2, 7, 5, 17, 25, 52, 71, with “L” and “H” on the back | Unapproved drug other |
| Chartwell RX (made by ECI) | 15, 16.2, 30, 32.4, 60, 64.8, 97.2, 100 | 691, 625, 692, 626, 693, 627, 628, 694, with “ECI” on the back | Unapproved drug other |
The two FDA approvals we found are recent and narrow: one for newborn babies and one for dogs.
| Date | Where | What happened |
|---|---|---|
| 1977 | WHO | Added to the Model List of Essential Medicines for epilepsy (added again in 2007 for status epilepticus) |
| November 17, 2022 | US (FDA) | Sezaby injection approved for seizures in term and preterm newborns |
| September 6, 2023 | US (FDA, animal drugs) | Fidoquel-CA1 tablets conditionally approved for dogs with epilepsy |
| June 29 to November 30, 2026 | Australia (TGA) | Phenobarbitone injection unavailable; an overseas product approved for supply instead |
Method note: In October 2026 we opened five US phenobarbital tablet labels on DailyMed (the four above plus one repackager’s label for ECI’s 64.8 mg tablet) and recorded each one’s marketing category, DEA schedule, strengths and imprints. This is a sample, not a count of every product. Dates come from the FDA, the WHO and the TGA.
Phenobarbital in our five countries
| Place | Name used | Legal status | Worth knowing |
|---|---|---|---|
| United States | Phenobarbital | Prescription only; DEA Schedule IV (C-IV) | Tablet labels say “unapproved drug”; Sezaby injection approved for newborns in 2022 |
| Puerto Rico | Phenobarbital | Same federal FDA and DEA rules as the US | No local difference found |
| Canada | Phenobarbital | Named in Schedule IV of the Controlled Drugs and Substances Act | Have a Canadian box? Search its DIN with our NDC and DIN lookup |
| Australia | Phenobarbitone or phenobarbital | Schedule 4, prescription only | Phenobarb 30 mg tablet (white, round, scored) is on the PBS; the injection is in short supply until November 30, 2026 |
| India | Phenobarbitone | Sold on prescription | Brands include Gardenal (Abbott India); 30 mg tablets have a government price cap |
Australia’s details come from healthdirect and the TGA. India’s price cap comes from a 2017 Department of Pharmaceuticals order under the Drugs (Prices Control) Order, 2013. India’s prescription status and the Gardenal brand come from a major Indian pharmacy listing, because we could not confirm phenobarbitone’s drug schedule from an official source.
How can you identify a phenobarbital tablet?
The US phenobarbital tablets we checked are all white and round, so check the imprint rather than the color or shape. Compare yours with pictures of phenobarbital pills or use our pill imprint search. If a refill looks different, read why your refill looks different and ask your pharmacist before taking it.
Common questions
Can you die from a phenobarbital overdose?
Yes, barbiturate poisoning can be life-threatening. A phenobarbital overdose can slow or stop breathing and cause shock and coma, and a long coma can cause permanent disability. Mixing it with alcohol, opioids or benzodiazepines makes it more dangerous, so call for help right away.
How long does phenobarbital stay in your system?
A long time. The label gives an average half-life of 79 hours in adults, so it takes more than three days for the body to clear half of it. After an overdose, MedlinePlus says recovery with proper treatment takes about 1 to 5 days.
Is phenobarbital a controlled substance?
Yes. It is a Schedule IV controlled substance in the US, it is named in Schedule IV of Canada’s Controlled Drugs and Substances Act, and it is a Schedule 4 prescription-only medicine in Australia. US labels warn it can cause dependence.
Does “unapproved” mean US phenobarbital is illegal or fake?
No. It means the FDA has not reviewed and approved those products, and the labels say so. They are still prescription medicines dispensed by pharmacies, so don’t stop taking phenobarbital on your own.
What happens if my dog takes too much phenobarbital?
Call your veterinarian, the ASPCA Animal Poison Control Center at (888) 426-4435, or Pet Poison Helpline at (855) 764-7661 right away. Both are open 24/7, and a fee may apply. Don’t wait for signs such as wobbling or deep sleep.
