phenobarbital vs primidone
Side-by-side comparison of phenobarbital and primidone Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Luminal
Mysoline
Phenobarbital is a medicine that can help control seizures and calm you down. It belongs to a class of drugs called barbiturates.
Primidone is a medicine used to control seizures. It belongs to a class of drugs called anticonvulsants.
This medicine is used to treat generalized and partial seizures. Seizures are caused by unusual electrical activity in the brain. Phenobarbital helps to reduce this activity and prevent seizures.
Primidone is used to manage grand mal, psychomotor, and focal epileptic seizures. It can be used alone or with other seizure medicines. It may help control grand mal seizures that don't respond to other treatments.
Phenobarbital works by slowing down the activity of your brain and nervous system. It increases the effects of a natural chemical in the body called GABA. This helps to reduce seizures and promote relaxation.
Primidone works in the brain to reduce the frequency of seizures. It is similar to a barbiturate and helps to stabilize electrical activity. This can help prevent seizures from starting.
- • Drowsiness
- • Sedation
- • Lethargy
- • Vertigo
- • Feeling unsteady
- • Dizziness
- • Drowsiness
- Medicine not working 2,389
- Seizure 1,534
- Using the medicine for a condition it is not approved for 1,358
- Medicine interacting with another medicine 635
- Poisoning from different things 621
- Medicine not working 814
- Falling down 651
- Tiredness 616
- Shaking 568
- Feeling lightheaded 484
You should not take this medicine if you are allergic to barbiturates. Also, do not take it if you have a history of porphyria, severe liver problems, or breathing problems.
You should not take primidone if you have porphyria or are allergic to phenobarbital.
Tell your doctor if you are pregnant or plan to become pregnant. Phenobarbital can harm an unborn baby. Talk to your doctor about the risks and benefits of taking this medicine while breastfeeding.
Talk to your doctor if you are pregnant or breastfeeding before taking primidone. This medicine can pass into breast milk and may harm your baby. Your doctor can help you weigh the risks and benefits.
How to Read This phenobarbital vs primidone Comparison
phenobarbital is classified in the Anticonvulsant (Barbiturate) drug class, while primidone sits within the Anticonvulsant (Barbiturate) class. Because both drugs share the same classification, they are often considered interchangeable in theory — but clinical outcomes rarely track that cleanly. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, phenobarbital has 6,537 submissions while primidone has 3,133. Those figures reflect cumulative reporting volume — not per-patient risk — so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot substitute for clinical judgment. Effectiveness, tolerability, drug-drug interactions with your other medications, kidney and liver function, pregnancy status, insurance formulary, and price all feed into a decision that only a licensed prescriber can make responsibly. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This page is for educational purposes only, is not medical advice, and should not be used to self-switch between phenobarbital and primidone — always consult your physician or pharmacist first.
Important: This comparison is for informational purposes only. Drug effects vary between individuals. Always consult your doctor or pharmacist for personalized medical advice.