Drug & supplement interaction

Chitosan + Acyclovir

Acyclovir brand names: Zovirax, Zovirax Injection, Sitavig, Avaclyr.

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

Chitosan has a moderate interaction with Acyclovir. Chitosan can reduce the absorption of acyclovir, potentially increasing the risk for treatment failure.

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

Chitosan and Acyclovir

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

Moderate

ACYCLOVIR (Zovirax)

Chitosan can reduce the absorption of acyclovir, potentially increasing the risk for treatment failure.
Clinical research in humans shows that taking chitosan along with acyclovir 200 mg reduces acyclovir absorption. Concomitant administration of chitosan 400 mg or 1000 mg reduced the acyclovir area under the curve (AUC) and peak plasma concentration by about 30% and 40%, respectively, compared with control. Concomitant administration with chitosan 1000 mg also increased time to peak concentration from 1 hour to 2 hours. In vitro research suggests that the mechanism for reduced absorption is due to acyclovir entrapment in chitosan-mucus complexes, which reduces intestinal absorption.
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 practical takeaway with chitosan and acyclovir. Chitosan is a fiber-like supplement that doesn't get digested. It can grab onto acyclovir in your gut and trap it in a gel-like mucus layer, so less of the medicine actually makes it into your bloodstream. A small human study found that chitosan cut acyclovir levels by roughly 30 to 40 percent and slowed down how fast it got absorbed.

Why does that matter? Acyclovir isn't a prodrug, so this isn't about activation. It's simply that less drug absorbed means a weaker antiviral effect, which could let a cold sore, shingles, or genital herpes outbreak heal more slowly or not respond as well. If you want to use both, the simplest fix is usually spacing them apart by a few hours. Please run the timing by your pharmacist or doctor first, and don't stop your acyclovir on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Kubbinga M, Nguyen MA, Staubach P, et al. The influence of chitosan on the oral bioavailability of acyclovir-a comparative bioavailability study in humans. Pharm Res 2015;32(7):2241-9. PubMed
  2. García MA, Hensler G, Al-Gousous J, Pielenhofer J, Wagner M, Lennernäs H, Langguth P. Novel food drug interaction mechanism involving acyclovir, chitosan and endogenous mucus. Drug Metab Pharmacokinet. 2023;49:100491. 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

Chitosan Also Interacts With Other Medications

Chitosan has 2 moderate known drug interactions in our database — the Acyclovir one above is one of them. If you take anything else, check it against the full list below.

Moderate 2 No known interaction 2,828 (incl. Acyclovir)
Taking anything else?

Check Another of Your Medications Against Chitosan

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

From our Q&A

Questions About Chitosan or Acyclovir

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

This page covers Chitosan only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Acyclovir page lists 37 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Siberian Cocklebur (major), African Wild Potato (moderate) and Aristolochia (moderate).

By severity: 3 major · 23 moderate · 11 minor.

From our pharmacist’s overview on the Acyclovir page

“Kidney strain is the risk to understand first. Acyclovir (Zovirax) can stress the kidneys on its own, and a few ingredients here, Siberian cocklebur especially, are toxic to kidney tissue, so pairing them could compound the harm.”

Reviewed by 2 · Jul 18, 2026

Open the Acyclovir interaction page

One more smart check

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

We hold 167 real supplement products containing Chitosan, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Chitosan. Your product may carry other ingredients that interact with Acyclovir too, on top of Chitosan — 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 Chitosan and Acyclovir 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 Chitosan
Top half

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

29 days ago today
Medication Acyclovir
Top 5%

#63 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 Chitosan

What is Chitosan?

Chitosan
  • Weight management
  • Lowering cholesterol
  • Wound care
  • General digestive supplement

Chitosan is a fiber-like substance made from the shells of shrimp, crabs, and other shellfish, often marketed for weight loss and cholesterol. The evidence for these benefits is weak, and any effects appear small at best. It is generally well tolerated for short-term use, but people with shellfish allergies and those who are pregnant or breastfeeding should be cautious.

Read the full Chitosan monograph & all interactions
Medication

About Acyclovir

What Is Acyclovir Used For?

Brand names: Zovirax, Zovirax Injection, Sitavig, Avaclyr

Acyclovir treats infections caused by herpes-family viruses. Which uses apply depends on the product and how it is given.

Oral acyclovir (capsules, tablets and suspension) is used for shingles, genital herpes and chickenpox. Creams, ointments, an eye ointment, a buccal tablet and an IV form each cover narrower uses, described below.

See full Acyclovir drug information
Keep checking

Other Drugs & Chitosan

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

0Major
2Moderate
0Minor
2,827No known interaction
2 Moderate 2,827 No interaction
Moderate

2 interactions

No interaction 2,827 drugs checked — show the list

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

Showing the 60 most looked-up of 2,827 medications checked with no known interaction — see the full Chitosan list.

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

Can you take Chitosan with Acyclovir?
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 Chitosan and Acyclovir 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 Acyclovir and Chitosan?

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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.