About this Drug Interaction Checker
PillsCard’s drug interaction checker analyzes 130,000+ substance-pair interactions and 547,000+ drug-pair combinations across our regulatory-sourced database. Every result shows the severity (critical, high, moderate, or low), mechanism (how the drugs interact at the molecular or organ level), and a clinical recommendation (what to do about it).
What counts as a drug interaction?
A drug-drug interaction (DDI) occurs when one medication changes another’s effect — either by altering how it’s absorbed, distributed, metabolized, or eliminated (pharmacokinetic), or by acting on the same receptor or system (pharmacodynamic). Interactions also include drug-food (e.g. grapefruit juice with statins), drug-supplement (St. John’s Wort with hormonal contraceptives), and drug-alcohol combinations. This tool focuses on drug-drug interactions; for food and alcohol see our medicine-alcohol guide and drug-food interactions guide.
Severity levels explained
- Critical— life-threatening interactions (e.g. MAOI + SSRI → serotonin syndrome, warfarin + ketorolac → major bleeding). Never combine without specialist supervision.
- High— clinically significant; requires close monitoring or alternative therapy (e.g. fluconazole + simvastatin → rhabdomyolysis risk).
- Moderate— dose adjustment or timing change usually resolves it (e.g. calcium supplements with levothyroxine — separate by 4 h).
- Low— minor effect, rarely clinically meaningful but worth knowing.
Where does the data come from?
We aggregate from four primary sources: FDA OpenFDA label data (US FDA), EMA Summary of Product Characteristics (European Medicines Agency), DDInter (peer-reviewed clinical pharmacology database from Tongji University), and SemMedDB (NIH semantic-mining of PubMed abstracts — ~3,500 evidence-based substance pairs). National regulators (URPL Poland, BfArM Germany, Swissmedic Switzerland, AIFA Italy, AEMPS Spain, KEGG Japan) contribute drug-label-level interaction sections. Data refreshes daily via automated parsers.
High-risk combinations to be aware of
Some combinations are known to cause severe adverse events — always check with this tool before combining:
- Warfarin + NSAIDs(ibuprofen, naproxen) — gastrointestinal bleeding risk increases up to 12-fold.
- MAOIs + serotonergic drugs(SSRIs, tramadol, triptans) — serotonin syndrome.
- Macrolides + statins(clarithromycin + simvastatin) — muscle toxicity.
- QT-prolonging combinations(e.g. azithromycin + amiodarone) — sudden cardiac death.
- Sildenafil + nitrates— severe hypotension.
Limitations
This tool reports known, documented interactions. It cannot account for your personal pharmacogenomics, kidney/liver function, age, or other medical context. Drugs from unverified sources, counterfeits, or compounded formulations may behave unpredictably. Always consult a pharmacist or physicianbefore adding, removing, or changing any medication based on this tool’s output.
Related tools and resources
- Drug Comparison — side-by-side comparison of two drugs (mechanism, dosing, side effects).
- Pill Identifier — identify a tablet by shape, color, or imprint.
- Symptoms Guide — what symptoms might mean and when to seek care.
- ICD-10 Codes — look up condition codes used in clinical practice.
- Health Blog — Pharmacist-reviewed articles on medication classes.