What the FDA labels say about taking them together
Cimetidine and tizanidine
Tizanidine's FDA label of January 2, 2026 names cimetidine in its drug interactions section; the cimetidine label PlainMeds reads does not name tizanidine. The tizanidine label: “… zileuton, fluoroquinolones other than strong CYP1A2 inhibitors, antiarrhythmics, cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.”
Check it at the source: the cimetidine FDA label on DailyMed (effective July 15, 2026, Mylan Pharmaceuticals Inc.); the tizanidine FDA label on DailyMed (effective January 2, 2026, Legacy Pharma USA, Inc.).
What does the cimetidine label say about tizanidine?
Cimetidine's label (effective July 15, 2026) does not name tizanidine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Cimetidine), Mylan Pharmaceuticals Inc., effective July 15, 2026 (SPL set 06c0a509-026f-44e0-9975-a94a8de51d43), via openFDA; the full label on DailyMed
What does the tizanidine label say about cimetidine?
Tizanidine label, drug interactionsConcomitant use of Zanaflex with moderate or weak CYP1A2 inhibitors (e.g., zileuton, antiarrhythmics [amiodarone, mexiletine, propafenone, and verapamil], cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Zanaflex label (Covis Pharma US, Inc, May 5, 2025), drug interactionsInhibitors other than Fluvoxamine and Ciprofloxacin Because of potential drug interactions, concomitant use of Zanaflex with other CYP1A2 inhibitors, such as zileuton, fluoroquinolones other than strong CYP1A2 inhibitors (which are contraindicated), antiarrhythmics (amiodarone, mexiletine, propafenone, and verapamil), cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Zanaflex label (Covis Pharma US, Inc, May 5, 2025), warnings and precautionsZanaflex may interfere with everyday activities; sedative effects of Zanaflex, alcohol, and other CNS depressants are additive ( 5.3 , 7.5 , 7.6 ) Hallucinations: consider discontinuation of Zanaflex ( 5.4 ) Less potent inhibitors of CYP1A2: may cause hypotension, bradycardia, or excessive drowsiness, use caution if Zanaflex is used with less potent inhibitors of CYP1A2, e.g., zileuton, other fluoroquinolones, antiarrhythmics, cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine ( 5.5 , 7.3 , 12.3 ) Renal impairment (creatinine clearance < 25 mL/min): use Zanaflex with caution, and monitor closely for dry mouth, somnolence, asthenia and dizziness as indicators of …
Ontralfy label (Rosemont Pharmaceuticals, LLC, October 25, 2025), drug interactionsConcomitant use of Ontralfy with moderate or weak CYP1A2 inhibitors (e.g., zileuton, antiarrhythmics [amiodarone, mexiletine, propafenone, and verapamil], cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Source: FDA drug label (Zanaflex, NDA020397), Covis Pharma US, Inc, effective May 5, 2025 (SPL set 043d9e51-bfa2-4add-9058-5ece332f7e99), via openFDA
Source: FDA drug label (Ontralfy, NDA216190), Rosemont Pharmaceuticals, LLC, effective October 25, 2025 (SPL set 7b88c338-c0b7-4c08-bef6-a4ffc2f25df7), via openFDA
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
| Cimetidine | Tizanidine | |
|---|---|---|
| Labeled for | Acid reflux and ulcers | Muscle spasms and spasticity |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.236 per tablet 300 mg tablet | $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