Interaction Checker

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A drug interaction checker that shows its sources

Add your medicines, supplements, and habits. Every result quotes the FDA prescribing label it came from, so you can see exactly what the manufacturer says before you talk to your pharmacist.

Open the checker
1,000+drugs, with 106,000+ documented interaction pairs
31supplements, foods, and habits, from alcohol and grapefruit to St. John's wort
0 bytesof your list sent anywhere. It stays in your browser

How it works

  1. Add what you takeSearch by brand or generic name. Supplements, foods like grapefruit, and habits like alcohol or caffeine count too. A drug that is not in the list can be looked up on demand from the FDA's own label database.
  2. Every pair is checkedEach combination is looked up in both manufacturers' FDA prescribing labels, read in both directions, and rated major, moderate, or minor based on the label's own language. Supplement and food rules come from NIH and FDA fact sheets.
  3. Read the exact quoteEvery rating links to the sentence it came from, with the label section it sits in and a link to the full document on DailyMed. Nothing is paraphrased.

What the ratings mean

Major

The label uses its strongest language: a contraindication, a boxed warning, or an instruction to avoid the combination. Talk to a prescriber before taking both.

Moderate

The label describes a meaningful effect and recommends monitoring, a dose change, or spacing the doses apart. Often manageable, rarely ignorable.

Minor

The label mentions the combination but describes the effect as small, or gives no instruction to avoid it or change the dose.

No interaction

The label explicitly reports no clinically significant interaction. Still worth confirming for your doses.

Sources

The primary source is the FDA prescribing label for each drug, retrieved from the openFDA drug label dataset, which mirrors the Structured Product Labeling documents published on DailyMed by the National Library of Medicine. Label text is a work of the U.S. government and is in the public domain. For each drug we choose one label: the reference (NDA or BLA) label where one exists, otherwise the most recent, most complete generic label. The chosen label, its effective date, and a DailyMed link are shown on every drug page.

Supplements, vitamins, foods, alcohol, and tobacco do not have FDA labels. For those we do two things: read the drug labels for mentions of them (labels frequently name alcohol, grapefruit, St. John's wort, antacids, and mineral supplements), and add a small set of curated rules taken from NIH Office of Dietary Supplements fact sheets, NCCIH herb pages, the FDA's consumer guidance on grapefruit, and the NIAAA's guidance on alcohol. Each rule cites the page it came from.

The matching method

  1. Sections. From each label we keep the boxed warning, contraindications, warnings and precautions (or the older warnings and precautions sections), and drug interactions. Pharmacokinetic tables are dropped. Adverse reaction lists, dosing, and clinical pharmacology are not scanned, because they rarely describe an actionable interaction.
  2. Terms. Every drug carries a set of name terms (generic name, salt form, and well-known brands) and class terms (for example "NSAID", "ACE inhibitor", "strong CYP3A4 inhibitor"). Classes come from our curated list and from the openFDA pharmacologic class fields where those are consistent across a drug's labels.
  3. Scan, both directions. For a pair A and B, each sentence of A's label is checked for B's terms, and each sentence of B's label for A's terms. Matching is whole-word, so "codeine" does not match "hydrocodone". When two drugs share a class, a class mention only counts if the sentence talks about "other" members of it, as in "other NSAIDs".
  4. Grade. A sentence in a boxed warning or contraindications section is Major. Elsewhere, wording such as contraindicated, avoid, not recommended, fatal, or serotonin syndrome is Major; monitor, dose, reduce, increase, or risk is Moderate; anything else is Minor. Sentences that say there was no clinically significant effect are graded as reporting no interaction. The pair's overall grade is the most severe sentence found.
  5. Show the work. Up to five sentences per label direction are displayed with the section they came from, the term that matched, and whether the match was by name or by class.

Coverage today

1,042 drugs and 31 supplements, foods, and habits are indexed, producing 106,459 pairs with documented evidence. Label data was exported from openFDA on 2026-10-07 and this site was generated on 2026-10-07. The checker can also look up any other drug with an FDA label on demand; those requests go from your browser straight to api.fda.gov.

Known limits

  • Labels are not exhaustive. A manufacturer documents what it studied or was required to warn about. A pair with nothing documented has not been shown to be safe.
  • Wording is graded by rule, not by a pharmacist. The grading rules are deliberate and consistent, but a sentence like "avoid abrupt discontinuation" will grade Major even when it is not about the other drug's danger. That is why the sentence is always shown.
  • Class matches can over-reach. A label that warns about "diuretics" applies to every diuretic in our list, including ones for which the risk is small.
  • One label per drug. Formulations differ. The label used is named on each page; an extended-release or topical product may carry different warnings.
  • Doses, timing, and your physiology are not modeled. Nothing here replaces a pharmacist's review of your actual regimen. Read the medical disclaimer.

Privacy

Your list is saved only in this browser and in the page address when you copy a link. Nothing you add is sent to a server, there is no account, and there are no ads or trackers. The one optional exception is the live FDA lookup, which sends the name you typed from your browser to api.fda.gov. Details in the privacy policy.

Questions

Where does the interaction data come from?
From the FDA prescribing labels published through openFDA and DailyMed. For each pair, the checker scans the boxed warning, contraindications, warnings, and drug interactions sections of both labels for a mention of the other drug by name or by drug class, and shows you the exact sentence. Supplement, food, and alcohol rules are drawn from NIH Office of Dietary Supplements and NCCIH fact sheets and FDA consumer guidance.
How is the severity decided?
By where the mention appears and how it is worded. A mention in a boxed warning or contraindications section, or wording such as contraindicated, avoid, or not recommended, is graded Major. Wording that calls for monitoring, a dose change, or spacing the doses is Moderate. A mention without an instruction is Minor. If the label explicitly reports no clinically significant interaction, the pair is marked accordingly.
What does it mean when nothing is documented?
It means neither label mentions the other drug or its class, and no curated rule applies. Labels are not exhaustive, so this is not proof that a combination is safe. Ask a pharmacist, especially for newer drugs or for more than a few medicines at once.
Can I check brand names, supplements, or alcohol?
Yes. Type a brand such as Tylenol, Zoloft, or Advil and the checker maps it to the generic. Supplements, vitamins, minerals, common foods such as grapefruit and dairy, alcohol, tobacco, and cannabis are included as items you can add to your list.
Is my medication list private?
Your list is kept in your browser's local storage and in the page address if you copy a link. It is never sent to our servers. The one exception is the optional FDA lookup for drugs outside our list, which queries api.fda.gov directly from your browser.
Is this a replacement for talking to a pharmacist?
No. This is a fast way to see what the official labels say before you ask. Dose, kidney and liver function, age, and other conditions change how an interaction matters, and only a clinician who knows your history can weigh that.

Who makes this

Interaction Checker is built and maintained independently. It is not affiliated with the FDA, the NIH, or any pharmaceutical company, and it has no sponsors and no advertising. Corrections and questions go to the contact address on the privacy page.

Method last updated 2026-09-23.