Drug & supplement interaction

Limosilactobacillus Reuteri + Cephalexin

Cephalexin brand names: Keflex, Keftab, Cephalex, Lexin.

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

Limosilactobacillus Reuteri has a moderate interaction with Cephalexin. Theoretically, taking Limosilactobacillus reuteri 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

Limosilactobacillus Reuteri and Cephalexin

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Cephalexin

Cephalexin falls under ANTIBIOTIC DRUGS — the group Limosilactobacillus Reuteri interacts with.

Theoretically, taking Limosilactobacillus reuteri with antibiotic drugs might decrease the effectiveness of L. reuteri.
L. reuteri 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. reuteri 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 key thing to know: this interaction works in one direction. Cephalexin (Keflex) won't be weakened by the probiotic, but the probiotic can be weakened by cephalexin. Since Keflex is an antibiotic that kills bacteria, it doesn't really tell the good guys from the bad guys. Taking your L. reuteri at the same time means the antibiotic may wipe out a chunk of those live organisms before they can do their job.

This is mostly theory based on how things work, not a dangerous interaction. Your infection treatment stays effective either way. A simple fix is to space them out by at least two hours. If you're using the probiotic for a specific reason, check with your pharmacist on timing.

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

Limosilactobacillus Reuteri Also Interacts With Other Medications

Limosilactobacillus Reuteri has 181 moderate known drug interactions in our database — the Cephalexin 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. Cephalexin)
Taking anything else?

Check Another of Your Medications Against Limosilactobacillus Reuteri

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

From our Q&A

Questions About Limosilactobacillus Reuteri or Cephalexin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Limosilactobacillus Reuteri or Cephalexin, 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 Cephalexin

This page covers Limosilactobacillus Reuteri only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Cephalexin page lists 61 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Siberian Cocklebur (major), African Wild Potato (moderate) and Aristolochia (moderate).

By severity: 3 major · 47 moderate · 11 minor.

From our pharmacist’s overview on the Cephalexin page

“Cephalexin (Keflex) is one of the most commonly prescribed oral antibiotics, usually for skin and urinary infections, and its supplement list warrants genuine care rather than a quick skim. Three of the 61 ingredients on file rate major.”

Reviewed by 2 · Jul 18, 2026

Open the Cephalexin interaction page

How much people look this up

Where Limosilactobacillus Reuteri and Cephalexin 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 Limosilactobacillus Reuteri
Steady interest

#1,130 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Cephalexin
Top 5%

#75 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 Limosilactobacillus Reuteri

What is Limosilactobacillus Reuteri?

  • Infant colic
  • Diarrhea (including antibiotic-associated)
  • Digestive health
  • Oral and gum health
  • Constipation
  • Immune support

Limosilactobacillus reuteri (formerly Lactobacillus reuteri) is a probiotic bacterium found in the human gut and certain fermented foods. It has the most supportive evidence for reducing crying in breastfed infants with colic and for some types of diarrhea, while many other uses remain unproven. It is generally well tolerated in healthy people, but people who are very ill or immunocompromised should talk to a doctor first.

Read the full Limosilactobacillus Reuteri monograph & all interactions
Medication

About Cephalexin

What Is Cephalexin Used For?

Brand names: Keflex, Keftab, Cephalex, Lexin

Cephalexin treats bacterial infections caused by susceptible strains of bacteria. It is used for respiratory tract infections, ear infections (otitis media), skin and skin structure infections, bone infections, and genitourinary tract infections — including acute prostatitis.

It works only against bacterial infections — not viruses like colds or flu. Your prescriber should use it only when a bacterial infection is confirmed or strongly suspected, to help prevent antibiotic resistance.

See full Cephalexin drug information
Keep checking

Other Drugs & Limosilactobacillus Reuteri

Browse every other medication we’ve checked against Limosilactobacillus Reuteri — 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 Limosilactobacillus Reuteri page.

No interaction 2,648 drugs checked — show the list

We also checked Limosilactobacillus Reuteri 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 Limosilactobacillus Reuteri list.

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

Can you take Limosilactobacillus Reuteri with Cephalexin?
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 Limosilactobacillus Reuteri and Cephalexin 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 Cephalexin and Limosilactobacillus Reuteri?

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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.