Herb & supplement monograph

Glucomannan Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Glucomannan interacts with medications. The heart of this page is the interaction list — every drug Glucomannan is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Glucomannan is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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On this page

Glucomannan Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, Glucomannan drug interactions pose a moderate risk for most people, because this thick, gel-forming fiber may reduce how much of a medication taken by mouth the body actually absorbs. Every listed interaction is rated moderate, and all of them trace back to this single absorption concern rather than to many separate drug problems.

Interactions deserving the most attention

The best-documented example is glyburide, a diabetes medicine: a small human study found lower drug levels in the blood when it was taken together with glucomannan. That makes diabetes medications the clearest place where this effect could matter, since less absorbed drug could mean less blood sugar control. In general, any oral medicine that needs steady, reliable levels deserves the most care with this supplement.

What the rest of the list means

The very large number of interactions can look alarming, but it reflects one broad concern applied to oral drugs as a group, not thousands of proven problems. For most medications the effect is theoretical, based on how viscous fiber behaves in the gut, and direct human evidence of a meaningful change exists for only one drug so far.

Check your medications against Glucomannan

Based on HelloPharmacist’s Glucomannan interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Glucomannan

2022 medications have a known interaction with Glucomannan, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Glucomannan using our pharmacist-reviewed interaction data.

AI summaries are generated from our Glucomannan interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. 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.
Possible. 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
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Glucomannan combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Glucomannan affects

Every type of medication (drug category) Glucomannan is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 1 drug category Glucomannan interacts with

Oral Drugs

Theoretically, glucomannan may decrease absorption of drugs taken orally.
Due to its viscosity and bulking effects, there is concern that glucomannan can decrease the absorption of oral drugs. A small clinical study in healthy volunteers shows that taking glyburide 2.5 mg plus glucomannan 3.9 grams with breakfast reduces plasma levels of glyburide when compared with breakfast and glyburide alone. In addition, animal research demonstrates this effect on amoxicillin, but shows increased absorption of metronidazole. This mouse model also demonstrates that metronidazole elimination is prolonged, but amoxicillin elimination is enhanced by 38%; glucomannan may also affect the distribution of some drugs. To avoid changes in absorption, take glucomannan 30-60 minutes after taking oral drugs.

Likelihood Probable Evidence B

Monograph

Glucomannan: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Glucomannan is a soluble fiber from the konjac root that swells into a gel in your stomach, which may help with mild weight loss, constipation, and modestly lowering cholesterol. It is generally well tolerated when taken with plenty of water, but it must be taken carefully because it can swell and cause choking or blockage if not swallowed properly. Talk with your pharmacist or doctor before starting it, especially if you have a health condition or take medicines.

Scientific name: Amorphophallus konjac
Family: Araceae
Part used: Root (tuber/corm)
Common forms: Capsules, tablets, powder, drink mixes; also used as a food ingredient (konjac noodles, shirataki noodles)

People commonly use it for

Weight loss and appetite control
Constipation
High cholesterol
Blood sugar support
Digestive health

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Generally well tolerated when taken with plenty of water, but it can cause choking or blockage if not swallowed properly.

PregnancyInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full pregnancy detail

BreastfeedingInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Glucomannan is a type of soluble dietary fiber that comes from the root (tuber) of the konjac plant, Amorphophallus konjac. This plant is native to parts of Asia, including Japan, China, and Southeast Asia, where the root has long been used as food.

When glucomannan is mixed with water, it absorbs a large amount of liquid and forms a thick, gel-like substance. Because of this property, it is widely used in supplements aimed at weight loss and digestive health, and it is also used as a thickener and gelling agent in foods such as konjac (shirataki) noodles.

You will find glucomannan in many over-the-counter products, including some popular brand-name weight-loss supplements.

How it works

Glucomannan is a long-chain soluble fiber that your body cannot digest. Its main effect comes from its ability to absorb water and swell into a thick gel in your stomach and intestines.

This gel may help in a few ways:

It adds bulk and slows down how quickly the stomach empties, which can make you feel full and may reduce how much you eat.
It adds bulk and moisture to stool, which can ease constipation.
It can bind to bile acids and reduce cholesterol absorption in the gut, which may lower blood cholesterol.
By slowing digestion, it may reduce how fast sugar enters the bloodstream after a meal.

Many of these mechanisms are supported by the general science of soluble fiber, but the exact size of these effects in people can vary.

Effectiveness

Does Glucomannan work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 8 uses evaluated

3 Possibly effective 5 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Possibly Effective Constipation