Drug & supplement interaction

Onion + Aspirin, Butalbital, Caffeine

Aspirin, Butalbital, Caffeine brand name: Fiorinal.

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

Aspirin, Butalbital, Caffeine falls into 2 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
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Onion and Aspirin, Butalbital, Caffeine

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Onion interacts with whole categories of medication. Aspirin, Butalbital, Caffeine falls into 2 of those categories, so it can interact with Onion in 2 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 2

Why this applies to Aspirin, Butalbital, Caffeine

Aspirin, Butalbital, 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

The piece of Fiorinal we care about here is the aspirin. Aspirin already makes your platelets less sticky, which is how it thins the blood a little. Lab studies suggest onion compounds (like quercetin) may do something similar and slow platelets down too. So in theory, pairing the two could add up and nudge your bleeding risk a bit higher, meaning easier bruising, nosebleeds, or stomach irritation.

I want to be honest about the evidence though: this is theoretical, based mostly on test-tube research, not real patients. Onion in your normal cooking is very unlikely to matter. The bigger question would be concentrated onion or quercetin supplements. If you're considering those, just check with 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

ASPIRIN

2 of 2
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 the thing to know about Fiorinal (aspirin, butalbital, and caffeine) and onion: this isn't about how your body breaks the medicine down. The aspirin part of Fiorinal doesn't change onion's metabolism, and onion doesn't change how aspirin works. Instead, the concern is allergy related. There's a single case report where someone with a mild onion allergy had their allergy flare up worse, with swelling and hives, after taking aspirin.

So if you don't have an onion allergy, this is very unlikely to affect you. Eating onion in normal food amounts shouldn't be a problem either. But if you do react to onion, mention it to your pharmacist or doctor before combining the two, since aspirin may make that reaction more intense. This is based on weak, anecdotal evidence, so don't panic, just be aware.

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 Aspirin, Butalbital, 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. Aspirin, Butalbital, 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 Aspirin, Butalbital, Caffeine

This page covers Onion only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Aspirin, Butalbital, Caffeine page lists 347 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 · 285 moderate · 49 minor.

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

“The aspirin inside Fiorinal (aspirin, butalbital, caffeine) is the reason this list deserves careful reading rather than a quick skim. More than 200 of the supplements and herbs on file can thin the blood further and raise bleeding risk on top of aspirin's own antiplatelet effect, and even ordinary alcohol, beer and wine included, carr…”

Reviewed by 2 · Jul 18, 2026

Open the Aspirin, Butalbital, 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 Aspirin, Butalbital, 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 Aspirin, Butalbital, 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%

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

29 days ago today
Medication Aspirin, Butalbital, Caffeine
Top 5%

#87 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
Medication

About Aspirin, Butalbital, and Caffeine

What Is Aspirin, Butalbital, and Caffeine Used For?

Brand name: Fiorinal

This combination is used to relieve the symptoms of tension (or muscle contraction) headache. The supported product is the oral capsule.

There is no evidence that it works or is safe for multiple recurrent headaches. Caution is needed because butalbital is habit-forming and can be abused.

See full Aspirin, Butalbital, and Caffeine drug information
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 Aspirin, Butalbital, 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 Aspirin, Butalbital, Caffeine supplement interactions › Every supplement checked against Aspirin, Butalbital, Caffeine, ranked by severity Aspirin, Butalbital, and Caffeine drug information › The full plain-English guide to this medication 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 Aspirin, Butalbital, Caffeine Together: Common Questions

Can you take Onion with Aspirin, Butalbital, 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 2 interactions listed for Onion and Aspirin, Butalbital, Caffeine?
Aspirin, Butalbital, 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 Aspirin, Butalbital, 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

Still Have a Question About Aspirin, Butalbital, Caffeine and Onion?

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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.