primidone
Brand names: Mysoline
Primidone is a medicine used to control seizures. It belongs to a class of drugs called anticonvulsants.
Drug Pricing (NADAC)
Brand Price
$62.56/unit
Generic Price
$1.25/unit
Generic Savings
98%
Generic Available
Yes (7 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Primidone is used to manage grand mal, psychomotor, and focal epileptic seizures.
Common side effects
Feeling unsteady, Dizziness, Drowsiness
Key warnings
You should not take primidone if you have porphyria or are allergic to phenobarbital.
How It Works
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.
How to Take It
If you are over 8 years old and haven't taken primidone before, start with a low dose. Follow your doctor's instructions carefully, increasing the dose slowly over several days. The usual maintenance dose for adults and children over 8 is 250 mg three or four times a day. Always follow your doctor's specific instructions.
Pregnancy & 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.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is close to your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store primidone at room temperature (68° to 77°F) in a tightly closed, light-resistant container.
Side Effects (from patient reports)
Based on 5,310 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 9,782 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2002–2025.
Total Reports
9,782
Death-Related Reports
850
Hospitalization Reports
3,062
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 813 |
| 2 | FALL | 651 |
| 3 | FATIGUE | 616 |
| 4 | TREMOR | 568 |
| 5 | DIZZINESS | 484 |
| 6 | DIARRHOEA | 480 |
| 7 | OFF LABEL USE | 476 |
| 8 | NAUSEA | 458 |
| 9 | HEADACHE | 385 |
| 10 | DRUG INTERACTION | 378 |
| 11 | SOMNOLENCE | 377 |
| 12 | ASTHENIA | 353 |
| 13 | DYSPNOEA | 349 |
| 14 | WEIGHT DECREASED | 321 |
| 15 | PAIN | 319 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
You should not take primidone if you have porphyria or are allergic to phenobarbital.
Known Drug Interactions
Anticonvulsants carbamazepine , phenobarbital, primidone, phenytoin ↓ nirmatrelvir/ritonavir Co-administration contraindicated due to potential loss of virologic response and possible resistance [see Contraindications (4) ] .
Mechanism: Primidone makes your body break down nirmatrelvir/ritonavir too fast, which lowers the amount of medicine in your blood. This can make the treatment stop working and help the virus become harder to treat.
What to do: Do not take these two medicines together. Your doctor will need to choose a different medication for you.
Drugs that have been shown, or that would be expected, to decrease plasma carbamazepine levels include cisplatin, doxorubicin HCl, felbamate, fosphenytoin, rifampin, phenobarbital, phenytoin, primidone, methsuximide, theophylline, aminophylline.
Mechanism: Primidone speeds up the liver's ability to break down carbamazepine, which lowers the amount of medicine in your blood.
What to do: Your doctor may need to monitor your blood levels or adjust your dose of carbamazepine.
7.5 Effects of Other Drugs on Folates Several drugs have been reported to reduce folate concentrations by inhibition of the dihydrofolate reductase enzyme (e.g., methotrexate and sulfasalazine) or by reducing folate absorption (e.g., cholestyramine), or via unknown mechanisms (e.g., antiepileptics such as carbamazepine, phenytoin, phenobarbital, primidone and valproic acid).
Mechanism: Primidone can lower the amount of folate (a B-vitamin) in your body through a process that is not yet fully understood.
What to do: Your doctor may recommend taking a folate supplement or checking your vitamin levels while on these medications.
Phenobarbital/Primidone ↓ lamotrigine Decreased lamotrigine concentration approximately 40%. ( 7 , 12.3 ) Carbamazepine, phenytoin, phenobarbital, primidone, and rifampin decrease lamotrigine concentrations by approximately 40%.
Mechanism: Primidone speeds up how fast your body breaks down lamotrigine, which lowers the amount of medicine in your blood.
What to do: Your doctor may need to increase your dose of lamotrigine to ensure it stays at a helpful level.
Drugs which may interact with folate include: • Antiepileptic drugs (AED): The AED class including, but not limited to, phenytoin, carbamazepine, primidone, valproic acid, fosphenytoin, valproate, phenobarbital and lamotrigine have been shown to impair folate absorption and increase the metabolism of circulating folate.
Mechanism: Primidone interferes with how your body absorbs folate and speeds up how fast your body uses up the folate in your system.
What to do: Talk to your doctor about monitoring your blood levels to ensure you are getting enough folate.
Common Questions
Can I stop taking primidone suddenly?
Will primidone interact with other medications I'm taking?
Can I drink alcohol while taking primidone?
How long does it take for primidone to start working?
What should I do if I experience side effects?
Can children take primidone?
Will primidone make me feel tired?
Does primidone cure epilepsy?
Can I take primidone if I have kidney problems?
Is it safe to drive while taking primidone?
What are the common side effects of primidone?
Does primidone interact with other medications?
What drug class is primidone?
Is there a generic version of primidone?
Is primidone safe during pregnancy?
Related Medications in Anticonvulsant (Barbiturate)
Other drugs grouped near primidone — same-class peers and common alternatives.
brivaracetam
Briviact
Brivaracetam is a medicine used to treat partial-onset seizures.
Compare with primidone →
cannabidiol
Epidiolex
Epidiolex is a medicine that contains cannabidiol.
Compare with primidone →
carbamazepine
Tegretol
Carbamazepine is a medicine used to control seizures and treat nerve pain.
Compare with primidone →
cenobamate
Xcopri
Xcopri is a medicine used to treat partial-onset seizures in adults.
Compare with primidone →
clobazam
Onfi, Sympazan
Clobazam oral suspension is a medicine used with other medicines to treat seizures caused by Lennox-Gastaut syndrome.
Compare with primidone →
Medication Guides
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What the FDA Data Shows for primidone
The FDA label for primidone (sold under brand names such as Mysoline) classifies it as a prescription-only medication in the Anticonvulsant (Barbiturate) class. Primidone is used to manage grand mal, psychomotor, and focal epileptic seizures. Official labeling lists 3 commonly reported side effects, including Feeling unsteady, Dizziness, Drowsiness.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 5,310 voluntary reports. The database also lists 9 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $1.25 versus $62.56 for the brand — a 98% generic savings.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: June 10, 2025
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages