Drug & supplement interaction

Lactobacillus Acidophilus + Ampicillin

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

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

Lactobacillus Acidophilus has a moderate interaction with Ampicillin. Theoretically, taking Lactobacillus acidophilus with antibiotic drugs might decrease the effectiveness of L.

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

Lactobacillus Acidophilus and Ampicillin

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Ampicillin

Ampicillin falls under ANTIBIOTIC DRUGS — the group Lactobacillus Acidophilus interacts with.

Theoretically, taking Lactobacillus acidophilus with antibiotic drugs might decrease the effectiveness of L. acidophilus.
L. acidophilus preparations usually contain live and active organisms. Therefore, simultaneously taking antibiotics might kill a significant number of the organisms. Tell patients to separate administration of antibiotics and L. acidophilus preparations by at least two hours.
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 keep in mind with this pairing: ampicillin doesn't become weaker, and neither does your treatment for the infection. The concern actually runs the other direction. Ampicillin kills bacteria, and it can't always tell the difference between the bad bugs causing your infection and the friendly Lactobacillus acidophilus you're swallowing as a probiotic. Take them at the same moment, and the antibiotic may wipe out a good chunk of those live cultures before they ever do their job.

This is a theoretical interaction based on how these two work, not something proven to cause harm, so don't lose sleep over it. A simple fix helps: space the probiotic at least two hours apart from your ampicillin dose. If you want to be sure of the timing, your pharmacist is happy to help.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pierce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York: The Stonesong Press, 1999:19.

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

Lactobacillus Acidophilus Also Interacts With Other Medications

Lactobacillus Acidophilus has 181 moderate 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.

Moderate 181 No known interaction 2,649 (incl. Ampicillin)
Taking anything else?

Check Another of Your Medications Against Lactobacillus Acidophilus

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

From our Q&A

Questions About Lactobacillus Acidophilus 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 Lactobacillus Acidophilus 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 Lactobacillus Acidophilus 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 Lactobacillus Acidophilus as Part of a Dietary Supplement Product? Check It for Interactions

We hold 6,180 real supplement products containing Lactobacillus Acidophilus, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Lactobacillus Acidophilus. Your product may carry other ingredients that interact with Ampicillin too, on top of Lactobacillus Acidophilus — 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 Lactobacillus Acidophilus 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 Lactobacillus Acidophilus
Top 5%

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

29 days ago today
Medication Ampicillin
Top half

#1,127 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 Lactobacillus Acidophilus

What is Lactobacillus Acidophilus?

Lactobacillus Acidophilus
  • Digestive health and balance
  • Diarrhea (including antibiotic-related)
  • Vaginal yeast and bacterial infections
  • Lactose intolerance
  • General immune support

Lactobacillus acidophilus is a 'friendly' bacterium used as a probiotic to support gut and vaginal health. It is generally well tolerated in healthy people, and there is reasonable evidence it may help with certain types of diarrhea, but proof for many other uses is limited. People with weakened immune systems or serious illness should check with a doctor before using it.

Read the full Lactobacillus Acidophilus 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 lining around the brain), septicemia (a serious bloodstream infection), and endocarditis (infection of the heart's inner lining).

Ampicillin capsules are specifically indicated for genitourinary tract infections — including gonorrhea — as well as meningitis caused by N. meningitidis. The injectable forms of Ampicillin and Ampicillin Sodium are reserved for moderate to severe infections or for patients who cannot take oral medication.

See full Ampicillin drug information
Keep checking

Other Drugs & Lactobacillus Acidophilus

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

0Major
181Moderate
0Minor
2,648No known interaction
181 Moderate 2,648 No interaction
Moderate

181 interactions

Showing 60 of 181 moderate interactions — see all 181 on the Lactobacillus Acidophilus page.

No interaction 2,648 drugs checked — show the list

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

Showing the 60 most looked-up of 2,648 medications checked with no known interaction — see the full Lactobacillus Acidophilus list.

See the full Lactobacillus Acidophilus 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
Lactobacillus Acidophilus 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 Lactobacillus Acidophilus and Ampicillin Together: Common Questions

Can you take Lactobacillus Acidophilus with Ampicillin?
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.
How serious is the Lactobacillus Acidophilus and Ampicillin 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 Ampicillin and Lactobacillus Acidophilus?

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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.