What the FDA labels say about taking them together
Cimetidine and theophylline
Cimetidine's FDA label of July 15, 2026 names theophylline in its drug interactions section, and theophylline's label names cimetidine too. The theophylline label: “Drug: Cimetidine; Type of Interaction: Decreases theophylline clearance by inhibiting cytochrome P450 1A2.; Effect**: 70% increase”
Check it at the source: the cimetidine FDA label on DailyMed (effective July 15, 2026, Mylan Pharmaceuticals Inc.); the theophylline FDA label on DailyMed (effective March 10, 2026, Strides Pharma Science Limited).
What does the cimetidine label say about theophylline?
Cimetidine label, drug interactionsDrug Interactions Cimetidine tablets, apparently through an effect on certain microsomal enzyme systems, has been reported to reduce the hepatic metabolism of warfarin-type anticoagulants, phenytoin, propranolol, nifedipine, chlordiazepoxide, diazepam, certain tricyclic antidepressants, lidocaine, theophylline, and metronidazole, thereby delaying elimination and increasing blood levels of these drugs.
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 theophylline label say about cimetidine?
Theophylline label, drug interactionsDrug: Cimetidine; Type of Interaction: Decreases theophylline clearance by inhibiting cytochrome P450 1A2.; Effect**: 70% increase
Theophylline label, warningsCessation of Smoking Drug Interactions: Adding a drug that inhibits theophylline metabolism (e.g., cimetidine, erythromycin, tacrine) or stopping a concurrently administered drug that enhances theophylline metabolism (e.g., carbamazepine, rifampin). (See PRECAUTIONS, Drug Interactions, Table II ).
Source: FDA drug label (Theophylline), Strides Pharma Science Limited, effective March 10, 2026 (SPL set b7a90ccf-9c32-40cc-9008-7e55b3da4dfd), 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 | Theophylline | |
|---|---|---|
| Labeled for | Acid reflux and ulcers | Asthma |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.236 per tablet 300 mg tablet | $0.330 per tablet 300 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