Drug & supplement interaction

Lacticaseibacillus Rhamnosus + Cephalexin

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

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

Lacticaseibacillus Rhamnosus has a moderate interaction with Cephalexin. Theoretically, taking Lacticaseibacillus rhamnosus 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

Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus interacts with.

Theoretically, taking Lacticaseibacillus rhamnosus with antibiotic drugs might decrease the effectiveness of L. rhamnosus.
L. rhamnosus 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. rhamnosus 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: it's not that the probiotic hurts your cephalexin, it's the other way around. Cephalexin is an antibiotic that kills bacteria, and Lacticaseibacillus rhamnosus is a live, beneficial bacterium. If you swallow them at the same time, the antibiotic can wipe out a good chunk of those probiotic organisms before they ever do their job. So your cephalexin still works fine against your infection, but the probiotic may not give you much benefit.

This is a theoretical concern based on how the two work, not a dangerous reaction. A simple fix is to space them out by at least two hours. If you're taking the probiotic to help with antibiotic-related diarrhea, ask your pharmacist about the best 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

Lacticaseibacillus Rhamnosus Also Interacts With Other Medications

Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus

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

From our Q&A

Questions About Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus
Steady interest

#1,007 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Cephalexin
Top 5%

#67 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 Lacticaseibacillus Rhamnosus

What is Lacticaseibacillus Rhamnosus?

  • Diarrhea (including antibiotic-related)
  • Digestive health
  • Vaginal and urinary health
  • Eczema and allergy prevention in children
  • Immune support

Lacticaseibacillus rhamnosus (often labeled L. rhamnosus GG) is a well-studied probiotic bacterium used mainly for diarrhea and general gut health. It is considered safe for most healthy people, with the best evidence for preventing certain types of diarrhea, but benefits for many other uses are uncertain. People who are seriously ill or have weakened immune systems should check with a doctor first.

Read the full Lacticaseibacillus Rhamnosus 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 & Lacticaseibacillus Rhamnosus

Browse every other medication we’ve checked against Lacticaseibacillus Rhamnosus — 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 Lacticaseibacillus Rhamnosus page.

No interaction 2,648 drugs checked — show the list

We also checked Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus list.

See the full Lacticaseibacillus Rhamnosus 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
Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus and Cephalexin Together: Common Questions

Can you take Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus 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 Lacticaseibacillus Rhamnosus?

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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.