Drug & supplement interaction

Guar Gum + Phentermine

Phentermine brand names: Adipex-P, Fastin, T Diet, Phentride, Obenix, and others.

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

Guar Gum has a moderate interaction with Phentermine. 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 Phentermine

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

Moderate

ORAL DRUGS

Why this applies to Phentermine

Phentermine 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 the simple version: guar gum is a gel-forming fiber, and when you swallow it, it can soak up water and grab onto things in your stomach, including pills you take by mouth. With phentermine, the concern is that the gel could slow down or lower how much of the drug your body actually absorbs. Phentermine isn't a prodrug, so less absorption usually just means a weaker effect, in this case less appetite control, which is the whole reason you're taking it.

This is a possible interaction, not a sure thing, and it's mostly seen with concentrated fiber supplements rather than small food amounts. An easy fix is timing: take your phentermine first, then wait about 30 to 60 minutes before the guar gum. Run your schedule by your pharmacist or doctor before changing anything.

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 Phentermine 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. Phentermine)
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 Phentermine

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 Phentermine, 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 Phentermine

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

The most serious there right now: Activated Charcoal (major), Ephedra (major), Peyote (major), Rauvolfia Vomitoria (major) and Sida Cordifolia (major).

By severity: 5 major · 43 moderate · 13 minor.

From our pharmacist’s overview on the Phentermine page

“Ephedra is the pairing I most want anyone taking phentermine (Adipex-P) to know about. Phentermine is itself a stimulant appetite suppressant that raises heart rate and blood pressure, and ephedra piles the same cardiovascular strain on top of it.”

Reviewed by 2 · Jul 18, 2026

Open the Phentermine 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 Phentermine 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 Phentermine 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 half

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

29 days ago today
Medication Phentermine
Top 25%

#690 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 Phentermine

What Is Phentermine Used For?

Brand names: Adipex-P, Fastin, T Diet, Phentride, Obenix, Pbc Phentride, Pbw Phentride, Phentrol #3, Ionamin, Phentrol #6, Phentrol #2, Phentrol #5, Phentrol, Obermine, Phentermine, Suprenza

Phentermine is approved as a short-term addition to a weight-loss program — not a standalone treatment. It is used alongside reduced-calorie eating, increased physical activity, and behavior changes to help manage obesity in adults whose body mass index (BMI) is 30 kg/m² or higher, or 27 kg/m² or higher when other risk factors such as controlled high blood pressure, diabetes, or high cholesterol (hyperlipidemia) are also present.

All available phentermine products — including Adipex-P, Lomaira, and various generic capsules and tablets — share this same FDA-approved use. Lomaira tablets are specifically dosed to be taken three times daily before meals, while other formulations are generally taken once daily. Treatment is intended to last only a few weeks.

See full Phentermine 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 Phentermine, 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 Phentermine supplement interactions › Every supplement checked against Phentermine, ranked by severity Phentermine 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 Phentermine Together: Common Questions

Can you take Guar Gum with Phentermine?
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 Phentermine 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 Phentermine 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.