How we check drug interactions
This page explains exactly where our interaction information comes from, how severity levels are assigned, and what the checker can and cannot tell you.
1. Source data: FDA drug labels
Every interaction on this site is grounded in official FDA labeling: the prescribing information for prescription drugs and the Drug Facts label for over-the-counter products. We download current labels through openFDA and link to the same labels on DailyMed, the U.S. National Library of Medicine’s official label library.
For alcohol, we also use the National Institute on Alcohol Abuse and Alcoholism (NIAAA) guide to mixing alcohol with medicines.
2. Interaction rules
Our database groups 147 common medicines, supplements and substances into drug classes (for example, NSAIDs, SSRIs, opioids or blood thinners). We then maintain 80 interaction rules between classes, such as “opioids plus benzodiazepines” or “fluoroquinolone antibiotics plus calcium, iron or magnesium.”
Each rule must be backed by specific wording in an FDA label. Before anything is published, an automated check confirms that the cited label actually contains supporting text, and that quoted text is shown with each result. A small number of minor, practical rules (for example, spacing probiotics away from antibiotics) are based on general pharmacology; these are marked as having no specific label warning.
3. Severity levels
| Level | What it means |
|---|---|
| Avoid / serious | The label has a boxed warning, contraindication or strong warning against the combination, or it can cause serious harm such as dangerous sedation, major bleeding or toxic drug levels. |
| Use caution | The label advises caution, monitoring or a dose change. Often used together with precautions. |
| Minor | A small or timing-related effect that is usually easy to manage. |
| No known interaction | Neither label lists the other medicine or its class, and no rule matched. |
4. The role of AI
AI tools help us draft plain-English explanations and articles. They are never used to decide whether an interaction exists or how serious it is. Those decisions come only from the labeled data and rules described above, and every article is checked against the same rules the checker uses, so the two can never disagree.
5. Limits you should know about
- The checker covers 147 common medicines and substances, not every drug on the market.
- It checks pairs. It cannot weigh your dose, age, kidney or liver function, pregnancy or other conditions.
- “No known interaction” is not a guarantee of safety.
- Labels change. We refresh label data regularly, and each page shows when it was last updated.
6. Medical review
We are working to add review by a licensed pharmacist. Until then, every page is written from FDA labeling and lists its sources so you can verify it. If you spot an error, please tell us and we will correct it quickly.