What the FDA labels say about taking them together
Primaquine and tizanidine
Primaquine's FDA label of February 11, 2026 names tizanidine in its drug interactions section; the tizanidine labels PlainMeds reads (3) do not name primaquine. The primaquine label: “Effects of Primaquine on the Pharmacokinetics of Other Drugs CYP1A2 Substrates Published clinical and non-clinical reports indicate primaquine inhibits CYP1A2 enzyme activity and thus may lead to increased exposure of …”
Check it at the source: the primaquine FDA label on DailyMed (effective February 11, 2026, Sanofi-Aventis U.S. LLC); the tizanidine FDA label on DailyMed (effective January 2, 2026, Legacy Pharma USA, Inc.).
What does the primaquine label say about tizanidine?
Primaquine label, drug interactionsEffects of Primaquine on the Pharmacokinetics of Other Drugs CYP1A2 Substrates Published clinical and non-clinical reports indicate primaquine inhibits CYP1A2 enzyme activity and thus may lead to increased exposure of CYP1A2 substrate drugs (e.g., duloxetine, alosetron, theophylline and tizanidine) when co-administered with Primaquine phosphate Tablets.
Source: FDA drug label (Primaquine Phosphate), Sanofi-Aventis U.S. LLC, effective February 11, 2026 (SPL set 1bfbf4ae-81b8-4160-a00d-6322aadd4b59), via openFDA; the full label on DailyMed
What does the tizanidine label say about primaquine?
Tizanidine's label (effective January 2, 2026) and its 2 other brand-application labels do not name primaquine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Zanaflex), Legacy Pharma USA, Inc., effective January 2, 2026 (SPL set 60c27d35-7349-4fc6-86ad-70fffdbe3e08), 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
| Primaquine | Tizanidine | |
|---|---|---|
| Labeled for | n/a | Muscle spasms and spasticity |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.0331 per tablet 4 mg tablet |
| 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