Drug & supplement interaction

Probiotics + Methenamine Mandelate

Methenamine Mandelate brand names: Mandelamine, Methimazole.

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

Probiotics has a moderate interaction with Methenamine Mandelate. Theoretically, taking antibiotic drugs with certain probiotics might decrease the effectiveness of probiotics.

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

Probiotics and Methenamine Mandelate

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Methenamine Mandelate

Methenamine Mandelate falls under ANTIBIOTIC DRUGS — the group Probiotics interacts with.

Theoretically, taking antibiotic drugs with certain probiotics might decrease the effectiveness of probiotics.
Many probiotics are bacteria. Since these preparations usually contain live and active organisms, simultaneously taking antibiotics might kill a significant number of sensitive organisms. Human research shows that taking probiotic concurrently with antibiotic treatment does not affect the diversity of the gut microbiome compared with antibiotic treatment in the absence of probiotics. Tell patients to separate administration of antibiotics and these 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: methenamine mandelate is a urinary antiseptic that works by turning into formaldehyde in acidic urine to fight bladder infections. The interaction on file isn't about your medicine getting weaker. It's the other way around. Because methenamine has germ-killing activity, taking it at the same time as a probiotic could knock out some of those live, friendly bacteria before they ever get going, so you may get less benefit from the probiotic itself.

This is a theoretical concern based on how these products work, and it's considered mild. A simple fix is to space them apart, ideally by at least two hours. Your methenamine should still do its job fine. If you're unsure about timing, just check with your pharmacist.

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
  3. Éliás AJ, Barna V, Patoni C, et al. Probiotic supplementation during antibiotic treatment is unjustified in maintaining the gut microbiome diversity: a systematic review and meta-analysis. BMC Med 2023;21(1):262. 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

Probiotics Also Interacts With Other Medications

Probiotics has 181 moderate, 40 minor known drug interactions in our database — the Methenamine Mandelate one above is one of them. If you take anything else, check it against the full list below.

Moderate 181 Minor 40 No known interaction 2,609 (incl. Methenamine Mandelate)
Taking anything else?

Check Another of Your Medications Against Probiotics

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

From our Q&A

Questions About Probiotics or Methenamine Mandelate

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

This page covers Probiotics only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Methenamine Mandelate page lists 91 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Ascophyllum Nodosum (moderate).

By severity: 4 major · 77 moderate · 10 minor.

From our pharmacist’s overview on the Methenamine Mandelate page

“People take methenamine mandelate (Mandelamine) day after day to keep urinary tract infections at bay, and that long habit is exactly why the 91 supplements on this page deserve genuine vigilance. Four carry a major rating, and most of those point at the liver: Siberian cocklebur has been linked to outright liver failure, and heavy bee…”

Reviewed by 2 · Jul 18, 2026

Open the Methenamine Mandelate interaction page

One more smart check

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

We hold 15 real supplement products containing Probiotics, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Probiotics. Your product may carry other ingredients that interact with Methenamine Mandelate too, on top of Probiotics — 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 Probiotics and Methenamine Mandelate 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 Probiotics
Top 25%

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

29 days ago today
Medication Methenamine Mandelate
Steady interest

#1,430 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 Probiotics

What is Probiotics?

  • Digestive health and regularity
  • Antibiotic-associated diarrhea
  • Irritable bowel syndrome (IBS)
  • Vaginal and urinary health
  • Immune support
  • General gut microbiome balance

Probiotics are live 'friendly' microbes that may help certain digestive conditions, such as antibiotic-associated diarrhea and some cases of IBS, though benefits depend heavily on the specific strain and dose. They are generally well tolerated for healthy people but should be used with caution by those with serious illness or weakened immune systems. Talk with your pharmacist or doctor to pick a product that matches your goal.

Read the full Probiotics monograph & all interactions
Medication

About Methimazole

What Is Methimazole Used For?

Brand names: Mandelamine, Methimazole

Methimazole tablets are used in adults and children with hyperthyroidism (an overactive thyroid) due to Graves' disease or toxic multinodular goiter when surgery or radioactive iodine is not the right option. They work to lower thyroid hormone levels and ease symptoms.

Methimazole tablets are also used to bring thyroid hormone levels down before a patient undergoes thyroidectomy (thyroid surgery) or radioactive iodine treatment, making those procedures safer.

See full Methimazole drug information
Keep checking

Other Drugs & Probiotics

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

0Major
181Moderate
40Minor
2,608No known interaction
181 Moderate 40 Minor 2,608 No interaction
Moderate

181 interactions

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

Minor

40 interactions

No interaction 2,608 drugs checked — show the list

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

Showing the 60 most looked-up of 2,608 medications checked with no known interaction — see the full Probiotics list.

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

Can you take Probiotics with Methenamine Mandelate?
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 Probiotics and Methenamine Mandelate 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 Methenamine Mandelate and Probiotics?

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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.