Drug & supplement interaction

Onion + Acetaminophen, Aspirin, Caffeine

Acetaminophen, Aspirin, Caffeine brand names: Excedrin Migraine, Excedrin, Excedrin Extra Strength.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Acetaminophen, Aspirin, Caffeine falls into 3 drug categories that Onion can interact with; the most serious is rated moderate. Theoretically, concomitant use of anticoagulant or antiplatelet drugs with onion might increase the risk of bleeding.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Onion and Acetaminophen, Aspirin, Caffeine

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Onion interacts with whole categories of medication. Acetaminophen, Aspirin, Caffeine falls into 3 of those categories, so it can interact with Onion in 3 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

1 of 3

Why this applies to Acetaminophen, Aspirin, Caffeine

Acetaminophen, Aspirin, Caffeine falls under ANTICOAGULANT/ANTIPLATELET DRUGS — the group Onion interacts with.

Theoretically, concomitant use of anticoagulant or antiplatelet drugs with onion might increase the risk of bleeding.
In vitro research shows that onion inhibits platelet aggregation.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the simple version. The aspirin in Excedrin already thins your blood a little by keeping platelets from clumping together. Lab studies suggest onion compounds (like quercetin and its sulfur compounds) may nudge platelets in the same direction. Put them together and, in theory, you could bleed or bruise a bit more easily, think nosebleeds, gums that bleed when you brush, or a cut that takes longer to stop.

I want to be honest, though: this concern comes from test-tube research, not real patients, and the everyday onion on your sandwich is very unlikely to matter. Concentrated onion supplements are the bigger question mark. If you take blood thinners or use Excedrin often, just run it by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  2. Hubbard, G. P., Wolffram, S., de Vos, R., Bovy, A., Gibbins, J. M., and Lovegrove, J. A. Ingestion of onion soup high in quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in man: a pil
Moderate

CYTOCHROME P450 2E1 (CYP2E1) SUBSTRATES

2 of 3

Acetaminophen, Aspirin, Caffeine also falls under CYTOCHROME P450 2E1 (CYP2E1) SUBSTRATES.

Theoretically, taking onion might increase the levels and clinical effects of drugs metabolized by CYP2E1.
Animal research shows that taking onion powder inhibits CYP2E1. However, this interaction has not been reported in humans.
Severity Moderate Likelihood Possible Evidence B

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist with Excedrin (acetaminophen, aspirin, and caffeine) and onion. One of the liver enzymes that helps process acetaminophen is called CYP2E1. In animal studies, concentrated onion powder seemed to slow that enzyme down a bit. In theory, slowing it could let a little more acetaminophen hang around in your system. The flip side is interesting too: CYP2E1 is the same pathway that creates the harmful byproduct behind acetaminophen liver injury, so blocking it isn't clearly a bad thing.

Honestly, this has only been seen in lab and animal work, never in real people, and normal amounts of onion in food won't matter. If you take concentrated onion supplements regularly, just mention it to your pharmacist so they can keep an eye on things.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Teyssier, C., Amiot, M. J., Mondy, N., Auger, J., Kahane, R., and Siess, M. H. Effect of onion consumption by rats on hepatic drug-metabolizing enzymes. Food Chem.Toxicol. 2001;39(10):981-987. PubMed
Moderate

ASPIRIN

3 of 3

Acetaminophen, Aspirin, Caffeine also falls under ASPIRIN.

Concomitant use of aspirin with onion may worsen onion allergy.
In one case report, a patient with a mild onion allergy reported worsening allergy, including swelling and severe urticaria, after taking aspirin.
Severity Moderate Likelihood Probable Evidence D

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's something worth knowing about combination products like Excedrin, which pack acetaminophen, aspirin, and caffeine into one pill. This isn't about onion changing how your body breaks down the medicine. Instead, there's a single, older case report where a person with a known onion allergy noticed their reaction got worse, with swelling and hives, after taking aspirin. The thinking is that aspirin may amplify an allergic response that was already there.

So if you don't have an onion allergy, this almost certainly doesn't apply to you, and normal food amounts of onion are not a concern. If you do react to onion and notice new swelling, itching, or hives after taking an aspirin product, check in with your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Eberhard P, Gall HM, Muller I, Moller R. Dramatic augmentation of a food allergy by acetylsalicylic acid. J Allergy Clin Immunol 2000;105:844 PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Onion Also Interacts With Other Medications

Onion has 274 moderate known drug interactions in our database — the Acetaminophen, Aspirin, Caffeine one above is among them. If you take anything else, check it against the full list below.

Moderate 274 No known interaction 2,556 (incl. Acetaminophen, Aspirin, Caffeine)
Taking anything else?

Check Another of Your Medications Against Onion

Covers the 2,830 medications we’ve checked against Onion. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Acetaminophen, Aspirin, Caffeine

This page covers Onion only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Acetaminophen, Aspirin, Caffeine page lists 371 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Beer (major), Danshen (major) and Ephedra (major).

By severity: 13 major · 312 moderate · 46 minor.

From our pharmacist’s overview on the Acetaminophen, Aspirin, Caffeine page

“Excedrin (acetaminophen, aspirin, and caffeine) packs three drugs into one tablet, which multiplies the ways supplements can collide with it, so treat this list with real care. Most entries involve the aspirin: hundreds of herbs add to its blood-thinning effect and raise bleeding risk, and even beer or wine earns a major rating for sto…”

Reviewed by 2 · Jul 18, 2026

Open the Acetaminophen, Aspirin, Caffeine interaction page

One more smart check

Taking Onion as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1,061 real supplement products containing Onion, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Onion. Your product may carry other ingredients that interact with Acetaminophen, Aspirin, Caffeine too, on top of Onion — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Onion and Acetaminophen, Aspirin, Caffeine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Onion
Top 25%

#242 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Acetaminophen, Aspirin, Caffeine
Top 25%

#396 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Onion

What is Onion?

Onion
  • Colds and respiratory symptoms
  • Heart and cholesterol health
  • Blood sugar support
  • Antimicrobial and wound care
  • Scar appearance (topical gels)

Onion is a common food with a long history in traditional medicine, and it contains antioxidants like quercetin and sulfur compounds. Eating onion as part of a balanced diet is safe for most people, but high-dose supplements have only limited human evidence for any specific health condition. Talk with your pharmacist or doctor before using concentrated onion products for a medical reason.

Read the full Onion monograph & all interactions
Keep checking

Other Drugs & Onion

Browse every other medication we’ve checked against Onion — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
274Moderate
0Minor
2,555No known interaction
274 Moderate 2,555 No interaction
Moderate

274 interactions

Showing 60 of 274 moderate interactions — see all 274 on the Onion page.

No interaction 2,555 drugs checked — show the list

We also checked Onion against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,555 medications checked with no known interaction — see the full Onion list.

See the full Onion interactions page
See every supplement checked against Acetaminophen, Aspirin, Caffeine, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Onion monograph › Uses, safety, and every drug interaction in one place Acetaminophen, Aspirin, Caffeine supplement interactions › Every supplement checked against Acetaminophen, Aspirin, Caffeine, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Onion and Acetaminophen, Aspirin, Caffeine Together: Common Questions

Can you take Onion with Acetaminophen, Aspirin, Caffeine?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 3 interactions listed for Onion and Acetaminophen, Aspirin, Caffeine?
Acetaminophen, Aspirin, Caffeine belongs to more than one drug category, and Onion interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Onion and Acetaminophen, Aspirin, Caffeine interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.