Drug & supplement interaction

Guar Gum + Psyllium (OTC drug)

Psyllium (OTC drug) brand name: Metamucil.

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

Guar Gum has a moderate interaction with Psyllium (OTC drug). Guar gum might reduce the absorption of some oral drugs, potentially decreasing their effectiveness.

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

Guar Gum and Psyllium (OTC drug)

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

Moderate

ORAL DRUGS

Why this applies to Psyllium (OTC drug)

Psyllium (OTC drug) falls under ORAL DRUGS — the group Guar Gum interacts with.

Guar gum might reduce the absorption of some oral drugs, potentially decreasing their effectiveness.
Clinical research shows that guar gum reduces or slows absorption of medications such as penicillin and metformin. To avoid changes in absorption, take guar gum 30-60 minutes after oral medications.
Severity Moderate Likelihood Possible Evidence B

Interaction 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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's a fun one: both guar gum and psyllium (Metamucil) are gel-forming soluble fibers that swell up in your gut. So we're really talking about taking two fibers together, not a classic drug-and-supplement clash. The interaction on file says guar gum can slow or reduce how the body absorbs certain oral medicines, but psyllium itself works inside the intestines to bulk up stool. It isn't a prodrug and doesn't need to be absorbed to do its job, so its laxative effect should still work.

The bigger practical concern is comfort and safety. Two thick, gel-forming fibers at once can mean more gas, bloating, and cramping, and without enough fluid they can raise the risk of choking or a blockage. Take each with a full glass of water, space them apart, and check with your pharmacist before doubling up on fiber.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Gin H, Orgerie MB, Aubertin J. The influence of Guar gum on absorption of metformin from the gut in healthy volunteers. Horm Metab Res 1989;21:81-3.
  2. Huupponen R, Seppala P, Iisalo E. Effect of guar gum, a fibre preparation, on digoxin and penicillin absorption in man. Eur J Clin Pharmacol 1984;26:279-81. 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

Guar Gum Also Interacts With Other Medications

Guar Gum has 2,024 moderate known drug interactions in our database — the Psyllium (OTC drug) one above is one of them. If you take anything else, check it against the full list below.

Moderate 2,024 No known interaction 806 (incl. Psyllium (OTC drug))
Taking anything else?

Check Another of Your Medications Against Guar Gum

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

From our Q&A

Questions About Guar Gum or Psyllium (OTC drug)

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Guar Gum or Psyllium (OTC drug), 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 Psyllium (OTC drug)

This page covers Guar Gum only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Psyllium (OTC drug) page lists 17 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Gum Arabic (moderate).

By severity: 1 major · 7 moderate · 9 minor.

From our pharmacist’s overview on the Psyllium (OTC drug) page

“Activated charcoal tops the psyllium (Metamucil) list and is the one entry rated major. Charcoal binds many medicines in the gut and can cut how much of them reaches the body, so pairing it with anything you take by mouth deserves real caution, and I would read that entry before the rest.”

Reviewed by 2 · Jul 18, 2026

Open the Psyllium (OTC drug) interaction page

One more smart check

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

We hold 33 real supplement products containing Guar Gum, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Guar Gum. Your product may carry other ingredients that interact with Psyllium (OTC drug) too, on top of Guar Gum — 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 Guar Gum and Psyllium (OTC drug) 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 Guar Gum
Top 25%

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

29 days ago today
Medication Psyllium (OTC drug)
Top half

#1,412 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 Guar Gum

What is Guar Gum?

Guar Gum
  • Constipation and bowel regularity
  • Diarrhea (as a stool bulking agent)
  • Lowering cholesterol
  • Blood sugar control
  • Feeling full for weight management

Guar gum is a soluble, gel-forming fiber from the guar bean that may modestly help with cholesterol, blood sugar, and bowel regularity. It is generally safe in food amounts, but concentrated supplements can cause gas, bloating, and a risk of throat or gut blockage if not taken with enough water. Always take it with plenty of fluid and check with your pharmacist or doctor first.

Read the full Guar Gum monograph & all interactions
Medication

About Psyllium

What Is Psyllium Used For?

Brand name: Metamucil

Psyllium is used to treat occasional constipation and help restore regularity. It is available under many brand names — including Careone, Best Choice, Premier Value Fiber, fiber laxative, meijer fiber laxative, Publix, Best Choice Fiber Therapy, Daily Fiber, Dr. Fibra, Lidl Orange Smooth Fiber Powder, and meijer fiber therapy — all for this same purpose.

Most products note that psyllium generally produces a bowel movement within 12 to 72 hours of taking a dose.

See full Psyllium drug information
Keep checking

Other Drugs & Guar Gum

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

0Major
2,024Moderate
0Minor
805No known interaction
2,024 Moderate 805 No interaction
Moderate

2,024 interactions

Showing 60 of 2,024 moderate interactions — see all 2,024 on the Guar Gum page.

No interaction 805 drugs checked — show the list

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

Showing the 60 most looked-up of 805 medications checked with no known interaction — see the full Guar Gum list.

See the full Guar Gum interactions page
See every supplement checked against Psyllium (OTC drug), 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
Guar Gum monograph › Uses, safety, and every drug interaction in one place Psyllium (OTC drug) supplement interactions › Every supplement checked against Psyllium (OTC drug), ranked by severity Psyllium 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 Guar Gum and Psyllium (OTC drug) Together: Common Questions

Can you take Guar Gum with Psyllium (OTC drug)?
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 Guar Gum and Psyllium (OTC drug) 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 Psyllium (OTC drug) and Guar Gum?

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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.