Drug & supplement interaction

Soy + Ampicillin

Ampicillin brand names: Principen, Omnipen-N, Omnipen, Rimacillin, Penbritin.

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

Soy has a minor interaction with Ampicillin. Theoretically, antibiotics may decrease the activity of soy isoflavones.

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

Soy and Ampicillin

Here is the interaction we found between these two, with the evidence behind it.

Minor

ANTIBIOTIC DRUGS

Why this applies to Ampicillin

Ampicillin falls under ANTIBIOTIC DRUGS — the group Soy interacts with.

Theoretically, antibiotics may decrease the activity of soy isoflavones.
Intestinal bacteria are responsible in part for converting soy isoflavones into their active forms. Antibiotics may decrease the amount of intestinal bacteria and decrease its ability to convert isoflavones.
Severity Minor 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 thing to understand: this interaction runs in one direction only. Ampicillin won't be affected by soy at all. Your antibiotic will still work just as well to fight off your infection, and soy doesn't change how ampicillin is absorbed or how strong it is.

What can happen is the reverse. Your gut bacteria help turn soy isoflavones into their active forms. Since ampicillin can knock back some of those helpful bacteria while you're taking it, you may get a little less benefit from soy during that short course. This is a theoretical, minor concern based only on lab and animal data, so don't worry about it. Enjoy your tofu or soy milk as usual, and check with your pharmacist if you take concentrated soy isoflavone supplements.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Morito K, Hirose T, Kinjo J, et al. Interaction of phytoestrogens with estrogen receptors alpha and beta. Biol Pharm Bull 2001;24:351-6. 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

Soy Also Interacts With Other Medications

Soy has 9 major, 343 moderate, 258 minor known drug interactions in our database — the Ampicillin one above is one of them. If you take anything else, check it against the full list below.

Major 9 Moderate 343 Minor 258 No known interaction 2,220 (incl. Ampicillin)
Taking anything else?

Check Another of Your Medications Against Soy

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

From our Q&A

Questions About Soy or Ampicillin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Soy or Ampicillin, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Ampicillin

This page covers Soy only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ampicillin page lists 50 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Bacillus Coagulans (moderate), Bacillus Subtilis (moderate), Bifidobacterium Animalis Subsp. Lactis (moderate) and Bifidobacterium Bifidum (moderate).

By severity: 1 major · 39 moderate · 10 minor.

From our pharmacist’s overview on the Ampicillin page

“An antibiotic only works if enough of it survives the trip through your gut, and that is where ampicillin (Principen, Penbritin) meets real trouble with one supplement in particular. Activated charcoal, the single major-rated entry among the 50 on this page, binds drugs in the digestive tract and can sharply cut how much ampicillin you…”

Reviewed by 2 · Jul 18, 2026

Open the Ampicillin interaction page

One more smart check

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

We hold 821 real supplement products containing Soy, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Soy. Your product may carry other ingredients that interact with Ampicillin too, on top of Soy — 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 Soy and Ampicillin 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 Soy
Top 25%

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

29 days ago today
Medication Ampicillin
Top half

#890 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 Soy

What is Soy?

  • Menopause symptoms (hot flashes)
  • Heart and cholesterol health
  • Bone health
  • Plant-based protein source
  • General nutrition

Soy is a nutritious bean that is a staple food and a popular source of plant protein and isoflavones. Eating soy foods as part of a balanced diet is generally considered safe for most people, and there is moderate evidence it may modestly help cholesterol and some menopause symptoms, though results vary. Talk with your pharmacist or doctor before using concentrated soy isoflavone supplements, especially if you have a history of hormone-sensitive conditions.

Read the full Soy monograph & all interactions
Medication

About Ampicillin

What Is Ampicillin Used For?

Brand names: Principen, Omnipen-N, Omnipen, Rimacillin, Penbritin

Ampicillin treats bacterial infections caused by susceptible organisms. It is used for respiratory tract infections, urinary tract infections, gastrointestinal infections (including typhoid fever and dysentery), bacterial meningitis (infection of the membranes surrounding the brain and spinal cord), and serious bloodstream infections such as septicemia and endocarditis (infection of the heart's inner lining).

Ampicillin capsules (oral form) are also indicated for genitourinary tract infections, including gonorrhea caused by non-penicillinase-producing organisms, and meningitis caused by N. meningitidis. The injectable forms (intramuscular or intravenous) are reserved for moderately severe to severe infections or for patients who cannot take oral medication.

See full Ampicillin drug information
Keep checking

Other Drugs & Soy

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

9Major
343Moderate
258Minor
2,219No known interaction
9 Major 343 Moderate 258 Minor 2,219 No interaction
Major

9 interactions

Moderate

343 interactions

Showing 60 of 343 moderate interactions — see all 343 on the Soy page.

Minor

258 interactions

Showing 60 of 258 minor interactions — see all 258 on the Soy page.

No interaction 2,219 drugs checked — show the list

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

Showing the 60 most looked-up of 2,219 medications checked with no known interaction — see the full Soy list.

See the full Soy interactions page
See every supplement checked against Ampicillin, 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
Soy monograph › Uses, safety, and every drug interaction in one place Ampicillin supplement interactions › Every supplement checked against Ampicillin, ranked by severity Ampicillin 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 Soy and Ampicillin Together: Common Questions

Can you take Soy with Ampicillin?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Soy and Ampicillin interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

Still Have a Question About Ampicillin and Soy?

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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.