Drug & supplement interaction

Bifidobacterium Animalis Subsp. Lactis + Metronidazole

Metronidazole brand names: Flagyl, Protostat, Metronidazole, Nidazol, Trikacide, and others.

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

Bifidobacterium Animalis Subsp. Lactis has a moderate interaction with Metronidazole. Theoretically, taking Bifidobacterium lactis with antibiotic drugs might decrease the effectiveness of B.

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

Bifidobacterium Animalis Subsp. Lactis and Metronidazole

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Metronidazole

Metronidazole falls under ANTIBIOTIC DRUGS — the group Bifidobacterium Animalis Subsp. Lactis interacts with.

Theoretically, taking Bifidobacterium lactis with antibiotic drugs might decrease the effectiveness of B. lactis.
Since B. lactis preparations usually contain live and active organisms, simultaneously taking antibiotics might kill a significant number of the organisms. Tell patients to separate administration of antibiotics and B. lactis preparations by at least 2 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: this interaction runs in one direction. Metronidazole (Flagyl) won't be weakened by the probiotic, but the probiotic can be weakened by the antibiotic. Metronidazole works by killing bacteria, and it can't tell the difference between the bug causing your infection and the friendly B. lactis in your supplement. So taking them at the same moment may wipe out a good chunk of those live organisms before they can help your gut.

This is a theoretical concern based on how the drug works, not a dangerous reaction. A simple fix is to space them out by at least 2 hours. Your metronidazole will still do its job, and many people use a probiotic during a course of antibiotics to ease stomach upset or diarrhea. Check with your pharmacist if you'd like timing tips.

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.
  2. Xiao JZ, Takahashi S, Odamaki T, et al. Antibiotic susceptibility of bifidobacterial strains distributed in the Japanese market. Biosci Biotechnol Biochem. 2010;74(2):336-42. 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

Bifidobacterium Animalis Subsp. Lactis Also Interacts With Other Medications

Bifidobacterium Animalis Subsp. Lactis has 181 moderate known drug interactions in our database — the Metronidazole 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. Metronidazole)
Taking anything else?

Check Another of Your Medications Against Bifidobacterium Animalis Subsp. Lactis

Covers the 2,830 medications we’ve checked against Bifidobacterium Animalis Subsp. Lactis. Pick one to open its full report.

From our Q&A

Questions About Bifidobacterium Animalis Subsp. Lactis or Metronidazole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Bifidobacterium Animalis Subsp. Lactis or Metronidazole, 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 Metronidazole

This page covers Bifidobacterium Animalis Subsp. Lactis only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metronidazole page lists 83 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Cesium (major) and Ephedra (major).

By severity: 7 major · 63 moderate · 13 minor.

From our pharmacist’s overview on the Metronidazole page

“Metronidazole (Flagyl) can stretch the heart's QT interval on its own, and most of the seven major-rated interactions among its 83 flagged supplement ingredients do the same thing, so I read this list with more wariness than most antibiotics earn. Grapefruit and ephedra stand out for adding to that heart-rhythm risk, while activated ch…”

Reviewed by 2 · Jul 18, 2026

Open the Metronidazole interaction page

How much people look this up

Where Bifidobacterium Animalis Subsp. Lactis and Metronidazole 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 Bifidobacterium Animalis Subsp. Lactis
Steady interest

#1,089 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Metronidazole
Top half

#750 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 Bifidobacterium Animalis Subsp. Lactis

What is Bifidobacterium Animalis Subsp. Lactis?

  • Digestive health and regularity
  • Constipation relief
  • Immune support
  • Antibiotic-associated diarrhea
  • General gut microbiome balance

Bifidobacterium animalis subsp. lactis is a well-studied probiotic bacterium commonly added to supplements and yogurts to support digestion and gut health. It appears generally safe for most healthy people, with the best evidence for improving bowel regularity, but benefits vary by person and strain. Talk with your pharmacist or doctor before starting it, especially if you have a weakened immune system or a serious illness.

Read the full Bifidobacterium Animalis Subsp. Lactis monograph & all interactions
Medication

About Metronidazole

What Is Metronidazole Used For?

Brand names: Flagyl, Protostat, Metronidazole, Nidazol, Trikacide, MetroGel, Flagyl IV, Metronidazole Redi-Infusion, Flagyl IV RTU, Metro IV, Anabact, Metrosa, Metrotop, Noritate, Rozex Cream, Rozex Gel, Zyomet, Likmez

Metronidazole treats three main types of infections. It's used for trichomoniasis (a sexually transmitted parasitic infection), amebiasis (an intestinal or liver infection caused by a parasite), and serious anaerobic bacterial infections — infections caused by bacteria that thrive without oxygen, which can affect the abdomen, skin, bones, lungs, and other areas.

Because sexual partners can pass trichomoniasis back and forth, both partners are typically treated at the same time, even if one has no symptoms.

See full Metronidazole drug information
Keep checking

Other Drugs & Bifidobacterium Animalis Subsp. Lactis

Browse every other medication we’ve checked against Bifidobacterium Animalis Subsp. Lactis — 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 Bifidobacterium Animalis Subsp. Lactis page.

No interaction 2,648 drugs checked — show the list

We also checked Bifidobacterium Animalis Subsp. Lactis 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 Bifidobacterium Animalis Subsp. Lactis list.

See the full Bifidobacterium Animalis Subsp. Lactis interactions page
See every supplement checked against Metronidazole, 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
Bifidobacterium Animalis Subsp. Lactis monograph › Uses, safety, and every drug interaction in one place Metronidazole supplement interactions › Every supplement checked against Metronidazole, ranked by severity Metronidazole 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 Bifidobacterium Animalis Subsp. Lactis and Metronidazole Together: Common Questions

Can you take Bifidobacterium Animalis Subsp. Lactis with Metronidazole?
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 Bifidobacterium Animalis Subsp. Lactis and Metronidazole 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 Metronidazole and Bifidobacterium Animalis Subsp. Lactis?

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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.