Interactive tool · FDA label data

Drug Interaction Checker

Select two medications below to check for a known interaction. Severity and the interaction text come from the FDA-approved drug labels themselves.

Data updated 2026-05-15

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.

Interaction severity in our database

How the 3,919 documented drug-drug pairs break down by FDA-labeled severity. Most interactions are minor; major pairs are the ones worth a pharmacist check.

Major 268 (7%)
Moderate 711 (18%)
Minor 2,940 (75%)

Source: FDA drug labeling (Structured Product Labeling). Severity reflects FDA labeling, not a per-patient risk estimate.

Notable high-severity interactions

A sample of major drug-drug interactions in our database, check any specific pair above for the full label text.

Major Check pair →
theophylline + metoprolol 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,...
Major Check pair →
nirmatrelvir/ritonavir + simvastatin HMG-CoA reductase inhibitors lovastatin, simvastatin ↑ lovastatin ↑ simvastatin Co-administration contraindicated due to potential for myopathy including rhabdomyolysis [see Contraindications (4) ] . If treatment with PAXLOVID is considered medically necessary, discontinue use of lovastatin and simvastatin at least 12 hours prior to initiation of PAXLOVID, during the 5 days of PAXLOVID treatment, and for 5 days after completing PAXLOVID.
Major Check pair →
itraconazole + isavuconazonium Antihelminthics, Antifungals and Antiprotozoals Isavuconazonium Contraindicated during and 2 weeks after itraconazole treatment.
Major Check pair →
darunavir + lovastatin Lipid Modifying Agents: HMG-CoA reductase inhibitors: lovastatin, simvastatin ↑ lovastatin ↑ simvastatin Co-administration is contraindicated due to potential for serious reactions such as myopathy including rhabdomyolysis.
Major Check pair →
clarithromycin + quetiapine Colchicine (in patients with normal renal and hepatic function) Use With Caution Antipsychotics: Pimozide Contraindicated Pimozide: [See Contraindications ( 4.2 )] Quetiapine Lurasidone Quetiapine: Quetiapine is a substrate for CYP3A4, which is inhibited by clarithromycin. Co‑administration with clarithromycin could result in increased quetiapine exposure and possible quetiapine related toxicities. Refer to quetiapine prescribing information for recommendations on dose reduction if co‑administered with CYP3A4 inhibitors such as clarithromycin.
Major Check pair →
ezetimibe + amlodipine For patients taking amiodarone, amlodipine, or ranolazine, do not exceed ezetimibe and simvastatin 10 mg/20 mg daily [see Dosage and Administration ( 2.3 )].
Major Check pair →
ezetimibe/simvastatin + amlodipine For patients taking amiodarone, amlodipine, or ranolazine, do not exceed VYTORIN 10/20 mg daily [see Dosage and Administration (2.3) ] .
Major Check pair →
simvastatin + diltiazem Intervention: For patients taking verapamil, diltiazem, or dronedarone, do not exceed ezetimibe and simvastatin 10 mg/10 mg daily.

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 shows the severity we derived plus the interaction text as it appears in the label. It does not tell you what to do about an interaction; that is a conversation for your prescriber or pharmacist.
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.