What the FDA labels say about taking them together
Metformin and zonisamide
Metformin's FDA label of September 3, 2026 names zonisamide in its drug interactions section; the zonisamide labels PlainMeds reads (3) do not name metformin. The metformin label: “Carbonic anhydrase inhibitors frequently cause a decrease in serum bicarbonate and induce non-anion gap, hyperchloremic metabolic acidosis. …”
Check it at the source: the metformin FDA label on DailyMed (effective September 3, 2026, Granules India Ltd); the zonisamide FDA label on DailyMed (effective June 4, 2026, Sun Pharmaceutical Industries, Inc.).
What does the metformin label say about zonisamide?
Metformin label, drug interactionsCarbonic Anhydrase Inhibitors Clinical Impact: Carbonic anhydrase inhibitors frequently cause a decrease in serum bicarbonate and induce non-anion gap, hyperchloremic metabolic acidosis. Concomitant use of these drugs with metformin hydrochloride extended-release tablets may increase the risk for lactic acidosis. Intervention: Consider more frequent monitoring of these patients. Examples: Topiramate, zonisamide, acetazolamide or dichlorphenamide.
Source: FDA drug label (Riomet, NDA021591), Sun Pharmaceutical Industries, Inc., effective December 6, 2018 (SPL set 05d4df4b-dfe8-4828-b423-a3d4f2c4114a), via openFDA
Source: FDA drug label (METFORMIN HYDROCHLORIDE), Granules India Ltd, effective September 3, 2026 (SPL set 73197cb5-3e23-4ac0-b189-f9bc848bce66), via openFDA; the full label on DailyMed
What does the zonisamide label say about metformin?
Zonisamide's label (effective June 4, 2026) and its 2 other brand-application labels do not name metformin in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Zonisamide), Sun Pharmaceutical Industries, Inc., effective June 4, 2026 (SPL set 3164d438-90bf-420a-9a56-5498b987f91c), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Metformin | Zonisamide | |
|---|---|---|
| Labeled for | Type 2 diabetes | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0145 per tablet 500 mg tablet | $0.106 per capsule 100 mg capsule |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once