Interactive tool · FDA label data

Drug Interaction Checker

Select two medications below to check for a known interaction, with severity, mechanism, and safety recommendations drawn from FDA drug labels.

Compiled by PlainMeds Editorial, Drug Information Editorial Team

3,919
Interactions tracked: 268
Major (high-severity): 711
Moderate: 682
Medications covered

Important: This tool is for informational purposes only. Always consult your healthcare provider or pharmacist before starting, stopping, or changing any medication.

Medication 1

Medication 2

Results: Theophylline + Metoprolol

Major Interaction between Theophylline and Metoprolol

FDA severity

Minor Be aware

Moderate Monitor or adjust

Major Generally avoid

Description

albuterol, systemic and inhaled mebendazole amoxicillin medroxyprogesterone ampicillin, with or without sulbactam methylprednisolone atenolol metronidazole azithromycin metoprolol caffeine, dietary ingestion nadolol cefaclor nifedipine co-trimoxazole (trimethoprim and sulfamethoxazole) nizatidine diltiazem norfloxacin dirithromycin ofloxacin enflurane omeprazole famotidine prednisone, prednisolone felodipine ranitidine finasteride rifabutin hydrocortisone roxithromycin isoflurane Sorbitol (purgative doses do not inhibit theophylline absorption) isoniazid sucralfate isradipine terbutaline,...

Mechanism

Metoprolol is a beta-blocker that can block the airway-opening effects of theophylline. This combination can make it harder for you to breathe and may change the amount of medicine in your blood.

Recommendation

Your doctor may need to adjust your dosages or monitor your blood levels closely. Report any new breathing difficulties to your healthcare provider immediately.

Based on interactions documented in FDA drug labeling. Label-documented interactions are not exhaustive, so a pharmacist checking a full clinical interaction database may find more. This is informational, not a clinical decision.

View Theophylline details View Metoprolol details Full interaction details

What does "Major" severity mean?

Major interactions may be life-threatening or cause serious side effects. These drug combinations should generally be avoided. Talk to your doctor immediately if you are taking both medications.

Frequently Asked Questions

How does the drug interaction checker work?

Select two medications from the dropdown menus and click "Check Interaction." The tool searches our database of FDA drug label data for known interactions between the two drugs and displays the severity, description, mechanism, and recommendation if an interaction exists.

What do the interaction severity levels mean?

Major interactions may be life-threatening or cause serious side effects and should generally be avoided. Moderate interactions may worsen your condition or change how your medications work, your doctor may need to adjust dosages. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.

What if no interaction is found?

If no interaction is found in our database, it does not guarantee that no interaction exists. Our database covers common prescription medications but may not include every possible drug combination. Always consult your doctor or pharmacist before combining medications.

Can I check more than two drugs at once?

This tool checks interactions between two specific drugs at a time. For checking multiple medications simultaneously, visit our full Interaction Checker at /interactions which supports adding multiple drugs.

Is this tool a substitute for medical advice?

No. This tool is for informational purposes only and should not replace professional medical advice. Always consult your healthcare provider or pharmacist before starting, stopping, or changing any medication.

Medical Disclaimer: This tool is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Drug interaction data is sourced from FDA drug labels and may not include all possible interactions. Always consult your doctor, pharmacist, or other qualified healthcare provider with any questions about your medications. Do not start, stop, or change any medication without professional medical advice.

Data source: U.S. Food and Drug Administration (FDA) drug labels via openFDA. The interaction set covers 3,919 documented drug-drug pairs across 682 medications, compiled from FDA Structured Product Labeling and last refreshed May 2026. See our methodology for source dates and how pairs are matched. Spot a pair that looks wrong? Report a correction.

Source: U.S. Food and Drug Administration (FDA): drug labels (Drug Interactions sections), Structured Product Labeling via openFDA. U.S. Food and Drug Administration (FDA): drug labels (Drug Interactions sections), Structured Product Labeling via openFDA.