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: Nirmatrelvir/Ritonavir + Simvastatin

Major Interaction between Nirmatrelvir/Ritonavir and Simvastatin

FDA severity

Minor Be aware

Moderate Monitor or adjust

Major Generally avoid

Description

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.

Mechanism

This medicine stops your body from breaking down simvastatin, which can lead to high levels that cause serious muscle damage.

Recommendation

Stop taking simvastatin at least 12 hours before starting Paxlovid and do not start it again until 5 days after you finish the treatment.

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 Nirmatrelvir/Ritonavir details View Simvastatin 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.