Drug & supplement interaction

Glucomannan + Peginterferon alfa-2a, Ribavirin

Peginterferon alfa-2a, Ribavirin brand names: Pegasys, Pegetron.

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

Glucomannan has a moderate interaction with Peginterferon alfa-2a, Ribavirin. Theoretically, glucomannan may decrease absorption of drugs taken orally.

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

Glucomannan and Peginterferon alfa-2a, Ribavirin

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

Moderate

ORAL DRUGS

Why this applies to Peginterferon alfa-2a, Ribavirin

Peginterferon alfa-2a, Ribavirin falls under ORAL DRUGS — the group Glucomannan interacts with.

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.
Severity Moderate Likelihood Probable Evidence B

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 combo. Glucomannan works by soaking up water and turning into a thick gel in your gut. That gel can wrap around pills you swallow and slow down or reduce how much of them gets absorbed. So the main concern here is with ribavirin, which is the oral capsule or tablet part of your hepatitis C treatment. If glucomannan blunts how much ribavirin you absorb, you could get less of the medicine you need to keep the virus in check.

Good news: the peginterferon (Pegasys) is an injection, so the fiber won't touch that part. To stay safe, a simple fix is to space them out, taking your ribavirin first and waiting 30 to 60 minutes before glucomannan. Please run this past your pharmacist or doctor before mixing them, since steady drug levels really matter for clearing hepatitis C.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Shima K, Tanaka A, Ikegami H, et al. Effect of dietary fiber, glucomannan, on absorption of sulfonylurea in man. Horm Metab Res 1983;15:1-3. PubMed
  2. Zhang Y, Aldamarany WAS, Song G, et al. Influence of konjac glucomannan and its derivatives on the oral pharmacokinetics of antimicrobial agent in antibiotics cocktails: Keep vigilant on dietary fiber supplement. Int J Biol Macromol 2023;251:126306. 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

Glucomannan Also Interacts With Other Medications

Glucomannan has 2,021 moderate known drug interactions in our database — the Peginterferon alfa-2a, Ribavirin one above is one of them. If you take anything else, check it against the full list below.

Moderate 2,021 No known interaction 809 (incl. Peginterferon alfa-2a, Ribavirin)
Taking anything else?

Check Another of Your Medications Against Glucomannan

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

Everything else you take

See Every Supplement That Interacts With Peginterferon alfa-2a, Ribavirin

This page covers Glucomannan only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Peginterferon alfa-2a, Ribavirin 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), Guar Gum (moderate) and Gum Arabic (moderate).

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

From our pharmacist’s overview on the Peginterferon alfa-2a, Ribavirin page

“Hepatitis C treatment with Pegasys or Pegetron (peginterferon alfa-2a plus ribavirin) is rough on the stomach, and the charcoal, fiber powders, and soothing gums people reach for are exactly what fills this list. All 17 entries work the same way, interfering with how the oral ribavirin half of the therapy gets absorbed.”

Reviewed by 2 · Jul 18, 2026

Open the Peginterferon alfa-2a, Ribavirin interaction page

One more smart check

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

We hold 467 real supplement products containing Glucomannan, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Glucomannan. Your product may carry other ingredients that interact with Peginterferon alfa-2a, Ribavirin too, on top of Glucomannan — 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 Glucomannan and Peginterferon alfa-2a, Ribavirin 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 Glucomannan
Top 25%

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

29 days ago today
Medication Peginterferon alfa-2a, Ribavirin
Top 25%

#302 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 Glucomannan

What is Glucomannan?

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

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.

Read the full Glucomannan monograph & all interactions
Medication

About Peginterferon Alfa-2a Injection

What Is Peginterferon Alfa-2a Injection Used For?

Brand names: Pegasys, Pegetron

Pegasys is used to treat chronic hepatitis C (CHC) in adults with compensated (stable) liver disease, typically in combination with other hepatitis C antiviral drugs. It is also approved for children 5 years and older with CHC in combination with ribavirin. Pegasys monotherapy (alone) is only an option when other HCV drugs cannot be used due to contraindications or serious intolerance.

Pegasys is also used to treat chronic hepatitis B (CHB) — both HBeAg-positive and HBeAg-negative types — in adults with compensated liver disease and evidence of active viral replication and liver inflammation. For children, Pegasys is approved for HBeAg-positive CHB in non-cirrhotic patients 3 years of age and older.

See full Peginterferon Alfa-2a Injection drug information
Keep checking

Other Drugs & Glucomannan

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

0Major
2,021Moderate
0Minor
808No known interaction
2,021 Moderate 808 No interaction
Moderate

2,021 interactions

Showing 60 of 2,021 moderate interactions — see all 2,021 on the Glucomannan page.

No interaction 808 drugs checked — show the list

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

Showing the 60 most looked-up of 808 medications checked with no known interaction — see the full Glucomannan list.

See the full Glucomannan interactions page
See every supplement checked against Peginterferon alfa-2a, Ribavirin, 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
Glucomannan monograph › Uses, safety, and every drug interaction in one place Peginterferon alfa-2a, Ribavirin supplement interactions › Every supplement checked against Peginterferon alfa-2a, Ribavirin, ranked by severity Peginterferon Alfa-2a Injection 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 Glucomannan and Peginterferon alfa-2a, Ribavirin Together: Common Questions

Can you take Glucomannan with Peginterferon alfa-2a, Ribavirin?
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 Glucomannan and Peginterferon alfa-2a, Ribavirin 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 Peginterferon alfa-2a, Ribavirin and Glucomannan?

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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.