6 Free Supplement Interaction Checkers (2026)

You can absolutely check supplement and medication interactions without paying — but you need to know where each free tool stops. The picks below are the same ones we reach for in our own household when a new bottle joins the cabinet. Most free web checkers were built for prescription drugs, so they are strong on medication-vs-medication and weak on the herbs, vitamins, and multi-ingredient supplements you actually want checked. This page names six free options, tells you honestly where each one falls short, and shows how to combine them so nothing slips through.

Before you decide

The real question behind “best free interaction checker” is usually: can I check my supplement plus my medication for free, without a pharmacist visit? The honest answer is “mostly, if you use more than one tool.”

Here is the gap that trips people up. The popular free web checkers — the ones that top the search results — are drug interaction checkers. They index prescription and over-the-counter medications very well. Supplements are a different, messier world: a single “sleep” or “immune” product can carry five or six botanical and vitamin ingredients, and free drug tools frequently return a thin result (or nothing) for those ingredients.

So the practical move is to split the job. Run your medications through a free drug checker, then look up each supplement ingredient against a trustworthy reference like the NIH’s NCCIH or MedlinePlus dietary supplements hub. The one tool below that tries to do both jobs at once — and reads the label for you — is our own app, disclosed as such.

6 free ways to check interactions

Feature sets on third-party tools change, so treat the descriptions below as a conservative snapshot — always confirm the current behavior on each site. We have flagged the single limitation most likely to matter for a supplement user, and who each tool suits best.

1. StackMyMed — free for your first 5 scans (our companion app)

What it is: an iOS app that uses your camera to scan a supplement or medication label, then checks your whole stack — every product together, not one pair at a time — and returns source-backed warnings, a dose timing and spacing view, and a PDF you can hand to a clinician.

What it is free for: your first 5 scans, at no cost — enough to run a real stack of a few supplements plus a medication and see the interactions.

The one limitation that matters: it is iOS-only and the free tier is capped at 5 scans, so it is not the tool for someone who wants an unlimited free web lookup. It is the only option here that reads your actual labels and checks the entire combination at once, but you pay after the free scans are used.

Best for: anyone taking several supplements alongside a medication who wants their real labels read and the full stack checked together, and who is fine on iPhone.

2. Drugs.com Interaction Checker — free, medication-focused

What it is: one of the most widely used free web interaction checkers. You add your medications by name and it returns interaction severity levels and plain-language explanations.

What it is free for: unlimited free web lookups of drug-vs-drug (and many OTC) interactions, with no login required for the basic checker.

The one limitation that matters: it is built around medications, so its coverage of individual botanical and vitamin supplement ingredients is comparatively thin — a multi-ingredient supplement may not resolve cleanly. Treat its supplement results as incomplete rather than authoritative.

Best for: a fast, free check of your prescription and OTC drug list. (We describe Drugs.com by name rather than linking it, because we could not confirm a stable public URL at publication — search “Drugs.com interaction checker” to reach the current tool.)

3. WebMD Interaction Checker — free, medication-focused

What it is: WebMD’s free interaction checker lets you build a list of drugs and see flagged interactions with severity and short explanations.

What it is free for: free web lookups of medication interactions, no payment required.

The one limitation that matters: like other drug-first tools, its supplement and herbal coverage is limited, and the free experience carries ads and consumer-health framing rather than clinical depth.

Best for: a quick second opinion to cross-check a drug interaction you already found elsewhere.

4. MedlinePlus (NIH / U.S. National Library of Medicine) — free reference, not a live checker

What it is: a free, government-run consumer health library. Its drug information, drug reactions, and dietary supplements pages explain what a substance is, common side effects, and known cautions.

What it is free for: unlimited free, ad-free, authoritative reference reading on both drugs and supplements.

The one limitation that matters: it is a reference library, not an interactive checker — you look substances up one at a time and read; it will not take your list and auto-flag pairwise interactions.

Best for: verifying what a free checker told you, and looking up supplement ingredients that drug tools skip.

5. NCCIH (National Center for Complementary and Integrative Health) — free supplement reference

What it is: the NIH center focused on herbs and dietary supplements. Its using supplements wisely guidance and per-herb pages are the closest free authority to “does this botanical interact with my medication.”

What it is free for: unlimited free reading on supplement safety and known drug-supplement cautions.

The one limitation that matters: like MedlinePlus, it is educational reference, not a tool that scans your stack — the work of matching each ingredient to each medication is on you.

Best for: filling the exact gap the drug checkers leave — the herb and botanical side of your stack.

6. FDA drug-interactions guidance — free official basics

What it is: the U.S. FDA’s free consumer page, Drug Interactions: What You Should Know, explaining how drug-drug, drug-food, and drug-supplement interactions happen.

What it is free for: free official background reading on interaction types and warning signs.

The one limitation that matters: it is orientation, not a lookup tool — it teaches you what to watch for but will not check your specific combination.

Best for: understanding why an interaction is flagged so you can ask your pharmacist the right question.

Free tools compared

No single free tool wins every column — that is the point of using more than one. The two reference libraries and the FDA page do not “scan” anything; the drug checkers scan drugs but not labels; only our own app reads a physical label and checks the whole combination.

How to actually check an interaction for free

Combining the free tools takes about five minutes and closes the supplement gap that any single tool leaves open.

1. List everything, including supplements. Write down every prescription, OTC medication, and supplement — and for multi-ingredient supplements, the individual ingredients from the label (this is the step drug checkers can’t do for you).
2. Run your medications through a free drug checker. Enter your drug list into a free web checker such as WebMD or Drugs.com and note any flagged pairs and their severity.
3. Cross-check each supplement ingredient against a free authority. Look up each herb or vitamin on NCCIH or MedlinePlus to catch the supplement-vs-drug cautions the drug checker missed. If you want the label read for you and the whole stack checked at once, StackMyMed’s free first 5 scans cover this step.
4. Confirm with a pharmacist. Bring your list (or the app’s PDF export) to a pharmacist — the free check tells you what to ask about; the pharmacist gives you the answer for your situation.

FAQ

Is there a free app to check supplement and medication interactions?

Yes. StackMyMed (our companion app) is free for your first 5 scans and is the only option here that reads your supplement labels and checks your whole stack together; for medication-only checks, the free Drugs.com and WebMD web checkers work well. Free drug-focused web checkers are weaker on supplements, so pair them with a free reference like NCCIH or MedlinePlus for the herbal and vitamin side.

Why do most free interaction checkers miss supplements?

Because they were built as drug interaction checkers and index medications far better than the many botanical and vitamin ingredients in supplements. A single supplement can contain several ingredients that the tool never resolves, so a “no interactions found” result on a supplement is not a guarantee of safety — it often just means the tool has no data on that ingredient.

Are free interaction checkers accurate enough to rely on?

They are a useful first pass, not a final answer. Free checkers can surface well-documented, high-severity drug interactions, but their databases differ, they update on their own schedules, and they can miss supplement interactions entirely. Treat any free result — a flag or an all-clear — as a prompt to confirm with a pharmacist before changing what you take.

This article is for education, not medical advice. It does not diagnose, treat, or replace care from a qualified professional. Interaction databases are incomplete and change over time, and an “all clear” from a free tool is not a guarantee of safety. Before starting, stopping, or combining any supplement or medication, confirm interactions with a pharmacist or your prescribing clinician.