zonisamide
Brand names: Zonegran
Zonisamide is a medicine used with other medicines to treat partial seizures in adults with epilepsy. It belongs to a class of drugs called anticonvulsants.
Drug Pricing (NADAC)
Generic Price
$0.10/unit
Generic Available
Yes (6 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Zonisamide is used to treat partial seizures in adults who have epilepsy.
Common side effects
Feeling sleepy, Loss of appetite, Dizziness
Key warnings
If you are allergic to sulfonamide medicines, you should not take zonisamide.
How It Works
Zonisamide works by slowing down the electrical signals in the brain that cause seizures. It is thought to stabilize nerve cell membranes, which reduces the chance of seizures. It may also affect certain chemicals in the brain.
How to Take It
Take zonisamide capsules by mouth once or twice a day. You can take it with or without food. Swallow the capsules whole; do not crush or chew them. Your doctor will start you on a low dose and slowly increase it every two weeks.
Pregnancy & Breastfeeding
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if zonisamide will harm your unborn baby. Talk to your doctor about the risks and benefits of taking zonisamide during pregnancy. It is also not known if zonisamide passes into breast milk, so talk to your doctor before breastfeeding.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and take your next dose at the regular time.
Storage
Store zonisamide capsules at room temperature (68°F to 77°F) in a dry place, away from light.
Side Effects (from patient reports)
Based on 8,191 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 14,210 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
14,210
Death-Related Reports
869
Hospitalization Reports
4,400
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 1,636 |
| 2 | SEIZURE | 1,574 |
| 3 | OFF LABEL USE | 872 |
| 4 | FATIGUE | 697 |
| 5 | SOMNOLENCE | 645 |
| 6 | CONVULSION | 623 |
| 7 | DIZZINESS | 558 |
| 8 | NAUSEA | 550 |
| 9 | HEADACHE | 543 |
| 10 | FALL | 496 |
| 11 | DRUG INTERACTION | 466 |
| 12 | CONDITION AGGRAVATED | 447 |
| 13 | VOMITING | 438 |
| 14 | DIARRHOEA | 412 |
| 15 | EPILEPSY | 378 |
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
If you are allergic to sulfonamide medicines, you should not take zonisamide. Using zonisamide with other medicines that also inhibit carbonic anhydrase (like topiramate) can increase the risk of metabolic acidosis, kidney stones, and high ammonia levels in the blood.
Known Drug Interactions
Examples: Topiramate, zonisamide, acetazolamide or dichlorphenamide Drugs that Reduce Metformin Clearance Clinical Impact: Concomitant use of drugs that interfere with common renal tubular transport systems involved in the renal elimination of metformin (e.g., organic cationic transporter-2 [OCT2]/multidrug and toxin extrusion [MATE] inhibitors) could increase systemic exposure to metformin and may increase the risk for lactic acidosis [see Clinical Pharmacology (12.3) ] .
Mechanism: Zonisamide interferes with how your kidneys remove metformin from your body, which can increase the risk of a serious condition called lactic acidosis.
What to do: Use these drugs together with caution and follow your doctor's advice on monitoring your health.
7 DRUG INTERACTIONS Table 3: Clinically Significant Drug Interactions with SEGLUROMET Carbonic Anhydrase Inhibitors Clinical Impact: The risk of lactic acidosis may increase due to concomitant use of Topiramate or other carbonic anhydrase inhibitors (e.g., zonisamide, acetazolamide or dichlorphenamide) with metformin.
Mechanism: Both drugs can cause a buildup of acid in the blood. Taking them together increases the risk of a serious condition called lactic acidosis.
What to do: Your doctor may need to monitor your blood levels more closely. Watch for symptoms like unusual tiredness or trouble breathing.
7.2 Other Carbonic Anhydrase Inhibitors Concomitant use of topiramate, a carbonic anhydrase inhibitor, with any other carbonic anhydrase inhibitor (e.g., zonisamide or acetazolamide) may increase the severity of metabolic acidosis and may also increase the risk of kidney stone formation.
Mechanism: Both drugs block the same enzyme, which can make your blood too acidic. This combination also makes it more likely that you will develop kidney stones.
What to do: Your doctor should monitor your blood chemistry closely. Make sure to drink plenty of fluids to reduce the risk of kidney stones.
In addition, carbamazepine causes, or would be expected to cause, decreased levels of the following drugs, for which monitoring of concentrations or dosage adjustment may be necessary: acetaminophen, albendazole, alprazolam, aprepitant, buprenorphone, bupropion, citalopram, clonazepam, clozapine, corticosteroids (e.g., prednisolone, dexamethasone), cyclosporine, dicumarol, dihydropyridine calcium channel blockers (e.g., felodipine), doxycycline, ethosuximide, everolimus, haloperidol, imatinib, itraconazole, lamotrigine, levothyroxine, methadone, methsuximide, mianserin, midazolam, olanzapin...
Mechanism: Carbamazepine speeds up how quickly your body breaks down zonisamide, which can make the zonisamide less effective.
What to do: Your doctor may need to monitor your blood levels or adjust your dose of zonisamide.
Table 4 Clinically Relevant Interactions with SYNJARDY or SYNJARDY XR Carbonic Anhydrase Inhibitors Clinical Impact Topiramate or other carbonic anhydrase inhibitors (e.g., zonisamide, acetazolamide or dichlorphenamide) frequently causes a decrease in serum bicarbonate and induce non-anion gap, hyperchloremic metabolic acidosis.
Mechanism: Zonisamide can cause a buildup of acid in your blood by lowering bicarbonate levels. Taking it with this medicine may increase the risk of this chemical imbalance.
What to do: Your doctor may need to monitor your blood tests more often. Tell your healthcare provider if you feel very tired or have trouble breathing.
Common Questions
Can I drink alcohol while taking zonisamide?
How long does it take for zonisamide to start working?
Can I stop taking zonisamide suddenly?
Does zonisamide cause weight loss?
Can zonisamide affect my thinking?
What should I do if I experience side effects?
Can I take zonisamide with other medications?
Will zonisamide cure my epilepsy?
What size capsules does zonisamide come in?
Where can I find more information about zonisamide?
What are the common side effects of zonisamide?
Does zonisamide interact with other medications?
What drug class is zonisamide?
Is zonisamide safe during pregnancy?
Related Medications in Anticonvulsant (Sulfonamide)
Other drugs grouped near zonisamide — same-class peers and common alternatives.
brivaracetam
Briviact
Brivaracetam is a medicine used to treat partial-onset seizures.
Compare with zonisamide →
cannabidiol
Epidiolex
Epidiolex is a medicine that contains cannabidiol.
Compare with zonisamide →
carbamazepine
Tegretol
Carbamazepine is a medicine used to control seizures and treat nerve pain.
Compare with zonisamide →
cenobamate
Xcopri
Xcopri is a medicine used to treat partial-onset seizures in adults.
Compare with zonisamide →
clobazam
Onfi, Sympazan
Clobazam oral suspension is a medicine used with other medicines to treat seizures caused by Lennox-Gastaut syndrome.
Compare with zonisamide →
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What the FDA Data Shows for zonisamide
The FDA label for zonisamide (sold under brand names such as Zonegran) classifies it as a prescription-only medication in the Anticonvulsant (Sulfonamide) class. Zonisamide is used to treat partial seizures in adults who have epilepsy. Official labeling lists 6 commonly reported side effects, including Feeling sleepy, Loss of appetite, Dizziness.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 8,191 voluntary reports. The database also lists 13 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $0.10.
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: August 1, 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