Phenobarbital
generic phenobarbital
Phenobarbital is a long-established treatment for epilepsy in dogs and cats. It is a human medicine and a controlled substance, filled at a licensed pharmacy on a vet’s prescription, with blood-level monitoring to set the dose.
What it is used for
Phenobarbital raises the seizure threshold and is one of the drugs a vet may start when a dog or cat has repeated seizures. It is given twice a day, every day, and the dose is adjusted against a blood level measured a couple of weeks after starting and after any change. Liver function is checked regularly because long-term use can affect it.
Sedation, wobbliness, increased thirst, hunger and urination are common early and often settle. Levetiracetam, potassium bromide and zonisamide are the usual alternatives or add-ons when phenobarbital alone does not control seizures or causes problems. Missing doses can trigger seizures, so it should never run out or be stopped suddenly.
Giving it to your pet
- How to give it
- At the same times every day, usually every 12 hours, with or without food. Consistency matters more than anything else with seizure control. It is a controlled substance, so plan refills well before you run out.
- If you miss a dose
- Give it as soon as you remember, unless it is nearly time for the next dose; in that case skip the missed dose and carry on as usual. Never give two doses at once to catch up. Never stop it suddenly; stopping a seizure medicine abruptly can trigger severe seizures, so your vet will reduce it gradually if needed.
- Storage
- At room temperature in a secure place, protected from light.
- Call your vet if you see
- Sleepiness and wobbliness are common in the first one to two weeks and usually ease. Increased thirst, urination and appetite are expected. Call your vet for yellowing of the gums or eyes, vomiting or loss of appetite, which can signal liver strain; your vet will check blood levels and liver values regularly.
Your vet’s instructions and the label on your pet’s medicine take priority over this general information.
Safety points that differ from human use
- Never stop or skip doses without the vet; sudden withdrawal can cause severe seizures.
- Phenobarbital speeds up the liver’s handling of many other drugs, so doses of other medicines may need adjusting.
- An overdose causes deep sedation and breathing depression; store it securely and call poison control if a quantity is eaten.
- Tablets (human)
- Oral elixir (human; contains alcohol)
- Compounded flavored liquids and capsules
- 15, 30, 60 and 100 mg tablets
- Compounded strengths to the vet’s prescription
Tablets come in enough strengths that most dogs can be dosed without compounding; cats often need a compounded liquid.
Why the cash price varies
Each pharmacy sets its own cash price, so quotes for the same phenobarbital prescription can differ. Because it is a Schedule IV controlled substance, refills are limited and the prescription has to be renewed regularly, so each renewal is a new fill. Checking before a refill is due that the pharmacy can supply the prescribed strength helps avoid running out.
Upload it and licensed pharmacies reply with their own cash price. You pay the pharmacy, not us.
How to pay less
- Ask the vet about the largest quantity per fill the rules allow, so refills come less often.
- Ask the vet to prescribe a tablet strength that fits the dose without compounding, and check that the pharmacy can supply it.
- If the pharmacy cannot supply the prescribed strength, the pharmacist may contact your vet; only the vet can change the prescription.
- Upload the prescription to Script Unlock so licensed pharmacies can quote. You pay the pharmacy directly.
Questions for your vet
- When will the blood level and liver tests be checked?
- What should I do if I miss a dose, or if my pet vomits after one?
- What should I do during a seizure, and when is a seizure an emergency?
- Does phenobarbital change the dose of my pet’s other medicines?
- How do I keep the prescription renewed so it never runs out?
Compare: Phenobarbital vs Keppra (levetiracetam) for dog seizures
Rules on refills, transfers and controlled substances differ by state; see pharmacy rules by state.
How Script Unlock gets you a cash price for your pet’s phenobarbital prescription
Prices on this site come from pharmacies responding to a real prescription. We do not publish estimated, average or "typical" prices, because none of those would be your price.
- 1You upload your prescription
A photo of your your pet’s phenobarbital prescription prescription is enough. Nothing is sold on the site; you are asking pharmacies to quote.
- 2Licensed pharmacies respond
Pharmacies that Script Unlock has verified see the request and each can reply with its own cash price for your exact drug, strength and quantity.
- 3You choose and pay the pharmacy
You compare the responses, pick a pharmacy, and pay that pharmacy directly when you collect. Script Unlock never takes a patient payment and never sets the price.
Related pet medications
Sources
- Merck Veterinary Manual
- ASPCA Animal Poison Control
- FDA Orange Book (approved generics and therapeutic equivalence)
- MedlinePlus drug information (National Library of Medicine)
Written by the Script Unlock editorial team from the sources above. Not yet reviewed by a veterinarian or veterinary pharmacist. Last checked 2026-10-03. Nothing here replaces your vet’s directions; doses for animals are set by weight and species.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.