Drug & supplement interaction

Horse Chestnut + Acyclovir

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

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Horse Chestnut and Acyclovir in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Horse Chestnut and Acyclovir

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Acyclovir and Horse Chestnut in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Horse Chestnut safety at a glance

Horse Chestnut overall Use caution Properly processed seed extract may be reasonably tolerated, but raw plant parts are toxic and the supplement isn't right for everyone.
Pregnancy Unsafe When the raw seed, bark, flower, or leaf are used orally. Horse chestnut preparations can be lethal; avoid using. There is insufficient reliable information ava... Read the full pregnancy detail
Breastfeeding Unsafe When the raw seed, bark, flower, or leaf are used orally. Horse chestnut preparations can be lethal; avoid using. There is insufficient reliable information ava... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Acyclovir and Horse Chestnut? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Acyclovir

Interactions in our licensed database are recorded against drug classes, not just single drug names. Acyclovir is filed under 6 classifications — including organic anion transporter 1 (oat1) substrates, topical drugs, nephrotoxic drugs. Horse Chestnut has documented interactions with 1 drug class — the most serious being anticoagulant/antiplatelet drugs (moderate) — and none of Acyclovir’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Horse Chestnut Does Interact With Other Medications

Horse Chestnut has 122 moderate known drug interactions in our database — Acyclovir isn’t one of them. If you take anything else, check it against the full list below.

Moderate 122 No known interaction 2,708 (incl. Acyclovir)
Taking anything else?

Check Another of Your Medications Against Horse Chestnut

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

What to actually watch for

No Interaction Found — But Data Suggests Horse Chestnut and Acyclovir May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Stomach pain / Nausea reported in 4.9% of FDA reports for Acyclovir Additional detail

    Horse Chestnut

    “Orally, there is one case report of pericardial tamponade following exudative pericardial effusion in a previously healthy 32-year-old male who consumed three boxes of horse chestnut paste over 6 weeks. The patient was treated with steroid therapy for 2 months, as well as colchicine 0.5 mg twice daily and ibuprofen 600 mg twice daily for 3 months.”

    Horse Chestnut · Natural Medicines adverse-effect record, reported in arrhythmia.

    2 sources cited
    1. 91972. Edem E, Kahyaoglu B, Çakar MA. Acute Effusive Pericarditis due to Horse Chestnut Consumption. Am J Case Rep. 2016;17:305-8. PubMed
    2. 110439. Yi HY, Lee JY. Poisoning due to consumption of horse chestnut seed. Clin Exp Emerg Med 2021;8(4):333-335. PubMed

    “Orally, horse chestnut seed extract has been reported to cause nausea, vomiting, diarrhea, abdominal pain, constipation, dry mouth, gastrointestinal upset, and dyspepsia.”

    Horse Chestnut · Natural Medicines adverse-effect record, reported in constipation.

    6 sources cited
    1. 282. Greeske K, Pohlmann BK. Horse chestnut seed extract-an effective therapy principle in general practice. Drug therapy of chronic venous insufficiency. Fortschr Med 1996;114:196-200.
    2. 12113. Pittler MH, Ernst E. Horse chestnut seed extract for chronic venous insufficiency (Cochrane Review). In: The Cochrane Library, Issue 3, 2004. Chichester, UK: John Wiley & Sons, Ltd. PubMed
    3. 55477. Ottillinger, B. and Greeske, K. Rational therapy of chronic venous insufficiency--chances and limits of the therapeutic use of horse-chestnut seeds extract. BMC.Cardiovasc.Disord. 2001;1(1):5. PubMed
    4. 55486. Pittler, M. H. and Ernst, E. Horse chestnut seed extract for chronic venous insufficiency. Cochrane.Database.Syst.Rev. 2004;(2):CD003230. PubMed
    5. 55493. Fang, Y., Zhao, L., Yan, F., Xia, X., Xu, D., and Cui, X. Escin improves sperm quality in male patients with varicocele-associated infertility. Phytomedicine. 2010;17(3-4):192-196. PubMed
    6. 55520. Rehn, D., Unkauf, M., Klein, P., Jost, V., and Lucker, P. W. Comparative clinical efficacy and tolerability of oxerutins and horse chestnut extract in patients with chronic venous insufficiency. Arzneimittelforschung 1996;46(5):483-487.

    Acyclovir

    Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • A skin rash reported in 3.7% of FDA reports for Acyclovir Additional detail

    Horse Chestnut

    “Pollen from the horse chestnut flower can cause allergic reactions in children. Horse chestnut can also cause hypersensitivity reactions, which occur more commonly in people who are allergic to latex.

    Rectally, the horse chestnut constituent esculin has caused severe allergic contact dermatitis and proctitis in a 38-year old man.

    Intravenously, administration of aescin can cause anaphylaxis (18,553).”

    Horse Chestnut · Natural Medicines adverse-effect record, reported in dermatitis.

    6 sources cited
    1. 7775. Popp W, Horak F, Jager S, et al. Horse chestnut (Aesculus hippocastanum) pollen: a frequent cause of allergic sensitization in urban children. Allergy 1992;47:380-3.
    2. 7853. Diaz-Perales A, Collada C, Blanco C, et al. Cross-reactions in the latex-fruit syndrome: A relevant role of chitinases but not of complex asparagine-linked glycans. J Allergy Clin Immunol 1999;104:681-7. PubMed
    3. 8418. Blanco C, Diaz-Perales A, Collada C, et al. Class I chitinases as potential panallergens involved in the latex-fruit syndrome. J Allergy Clin Immunol 1999;103:507-13. PubMed
    4. 10383. Comaish JS, Kersey PJ. Contact dermatitis to extract of horse chestnut (esculin). Contact Dermatitis 1980;6:150-1. PubMed
    5. 18. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.
    6. 553. Jaspersen-Schib R, Theus L, Guirguis-Oeschger M, et al. [Serious plant poisonings in Switzerland 1966-1994. Case analysis from the Swiss Toxicology Information Center]. Schweiz Med Wochenschr 1996;126:1085-98.

    Acyclovir

    Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Dizziness / Headache Additional detail

    Horse Chestnut

    “Orally, horse chestnut seed extract has been reported to cause headache or dizziness.”

    Horse Chestnut · Natural Medicines adverse-effect record, reported in cluster headache.

    2 sources cited
    1. 55486. Pittler, M. H. and Ernst, E. Horse chestnut seed extract for chronic venous insufficiency. Cochrane.Database.Syst.Rev. 2004;(2):CD003230. PubMed
    2. 55520. Rehn, D., Unkauf, M., Klein, P., Jost, V., and Lucker, P. W. Comparative clinical efficacy and tolerability of oxerutins and horse chestnut extract in patients with chronic venous insufficiency. Arzneimittelforschung 1996;46(5):483-487.

    Acyclovir

    Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir. Read the label on DailyMed ›

  • Vomiting Additional detail

    Horse Chestnut

    Recorded for Horse Chestnut in the same Natural Medicines adverse-effect record shown under Stomach pain / Nausea above.

    Acyclovir

    Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir. Read the label on DailyMed ›

Reported for Horse Chestnut but not commonly for Acyclovir: liver problems, stomach upset, an irregular heartbeat and an allergic reaction.

Effects for Acyclovir come from the ADVERSE REACTIONS section of its FDA label; effects for Horse Chestnut come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 114,761 voluntary FDA FAERS reports for Acyclovir that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Horse Chestnut in Pregnancy & Breastfeeding

Pregnancy And Lactation Unsafe

When the raw seed, bark, flower, or leaf are used orally. Horse chestnut preparations can be lethal; avoid using. There is insufficient reliable information available about the safety of horse chestnut seed extract when used during pregnancy and lactation; avoid using.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About Horse Chestnut 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 Horse Chestnut 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 Horse Chestnut 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 Horse Chestnut as Part of a Dietary Supplement Product? Check It for Interactions

We hold 487 real supplement products containing Horse Chestnut, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Horse Chestnut. Even though Horse Chestnut itself has no known interaction with Acyclovir, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Horse Chestnut 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 Horse Chestnut
Top 25%

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

29 days ago today
Medication Acyclovir
Top 5%

#59 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Horse Chestnut reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Horse Chestnut and Acyclovir records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Horse Chestnut

What is Horse Chestnut?

  • Chronic venous insufficiency
  • Leg swelling and heaviness
  • Varicose veins
  • Hemorrhoids
  • Bruising and minor swelling

Horse chestnut seed extract is most often used for chronic venous insufficiency, where standardized products may help reduce leg swelling, pain, and heaviness. Raw, unprocessed horse chestnut seeds and other parts of the plant are toxic and should never be eaten. Talk with your pharmacist or doctor before using it, and avoid it during pregnancy and breastfeeding.

Aesculus hippocastanum · Sapindaceae · Seeds (extract), and sometimes bark and leaves · Capsules, tablets, standardized seed extracts, topical gels and creams

An interaction check asks whether these two react with each other — it does not ask whether Horse Chestnut is a good idea for someone in your situation. Here is what our Horse Chestnut record says about it on its own.

Horse Chestnut: dosing

There is no single official dose for horse chestnut. Products are usually standardized to their aescin (escin) content, and the right amount depends on the specific product.The best approach is to follow the directions on the product label and choose a reputable, standardized extract.

From our Horse Chestnut monograph — the full record covers uses, side effects and every documented interaction.

Read the full Horse Chestnut monograph & all interactions
Medication

About Acyclovir

What Is Acyclovir Used For?

Brand names: Zovirax, Zovirax Injection, Sitavig, Avaclyr

Acyclovir treats infections caused by herpes viruses. Depending on the form, it is used for cold sores (herpes labialis), genital herpes (initial episodes and recurrent flare-ups), shingles (herpes zoster), and chickenpox (varicella). It can also be used long-term to suppress recurrent genital herpes outbreaks.

Some forms are approved for more serious situations: acyclovir injection is used in hospital settings for herpes simplex encephalitis (herpes infection of the brain), neonatal herpes (in newborns), and herpes or shingles infections in immunocompromised patients. Avaclyr ophthalmic ointment is specifically indicated for acute herpetic keratitis (a herpes ulcer on the cornea of the eye). Sitavig buccal tablet and Zovirax cream are specifically indicated for recurrent cold sores in immunocompetent adults.

Most-Reported Side Effects for Acyclovir

From FAERS, the FDA’s public side-effect reporting system (114,761 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 8,029 reports
Diarrhea 7,348 reports
Pneumonia 5,700 reports
Nausea 5,643 reports
Fever 4,989 reports
See full Acyclovir drug information
Keep checking

Other Drugs & Horse Chestnut

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

0Major
122Moderate
0Minor
2,707No known interaction
122 Moderate 2,707 No interaction
Moderate

122 interactions

Showing 60 of 122 moderate interactions — see all 122 on the Horse Chestnut page.

No interaction 2,707 drugs checked — show the list

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

Showing the 60 most looked-up of 2,707 medications checked with no known interaction — see the full Horse Chestnut list.

See the full Horse Chestnut interactions page
See every supplement checked against Acyclovir, ranked by severity
Evidence & sources

Horse Chestnut References

The 21 references that drive our Horse Chestnut monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Trans. S. Klein. Boston, MA: American Botanical Council, 1998.
  2. Ellenhorn MJ, et al. Ellenhorn's Medical Toxicology: Diagnoses and Treatment of Human Poisoning. 2nd ed. Baltimore, MD: Williams & Wilkins, 1997.
  3. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.
  4. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  5. Greeske K, Pohlmann BK. Horse chestnut seed extract-an effective therapy principle in general practice. Drug therapy of chronic venous insufficiency. Fortschr Med 1996;114:196-200.
  6. Robbers JE, Tyler VE. Tyler's Herbs of Choice: The Therapeutic Use of Phytomedicinals. New York, NY: The Haworth Herbal Press, 1999.
  7. Takegoshi K, Tohyama T, Okuda K, et al. A case of Venoplant-induced hepatic injury. Gastroenterol Jpn 1986;21:62-5.
  8. Jaspersen-Schib R, Theus L, Guirguis-Oeschger M, et al. [Serious plant poisonings in Switzerland 1966-1994. Case analysis from the Swiss Toxicology Information Center]. Schweiz Med Wochenschr 1996;126:1085-98.
  9. Popp W, Horak F, Jager S, et al. Horse chestnut (Aesculus hippocastanum) pollen: a frequent cause of allergic sensitization in urban children. Allergy 1992;47:380-3.
  10. Diaz-Perales A, Collada C, Blanco C, et al. Cross-reactions in the latex-fruit syndrome: A relevant role of chitinases but not of complex asparagine-linked glycans. J Allergy Clin Immunol 1999;104:681-7. PubMed
  11. Blanco C, Diaz-Perales A, Collada C, et al. Class I chitinases as potential panallergens involved in the latex-fruit syndrome. J Allergy Clin Immunol 1999;103:507-13. PubMed
  12. Comaish JS, Kersey PJ. Contact dermatitis to extract of horse chestnut (esculin). Contact Dermatitis 1980;6:150-1. PubMed
  13. Pittler MH, Ernst E. Horse chestnut seed extract for chronic venous insufficiency (Cochrane Review). In: The Cochrane Library, Issue 3, 2004. Chichester, UK: John Wiley & Sons, Ltd. PubMed
  14. Ottillinger, B. and Greeske, K. Rational therapy of chronic venous insufficiency--chances and limits of the therapeutic use of horse-chestnut seeds extract. BMC.Cardiovasc.Disord. 2001;1(1):5. PubMed
  15. Pittler, M. H. and Ernst, E. Horse chestnut seed extract for chronic venous insufficiency. Cochrane.Database.Syst.Rev. 2004;(2):CD003230. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Horse Chestnut and Acyclovir Together: Common Questions

Is it safe to take Horse Chestnut with Acyclovir?
We do not list a known interaction between Horse Chestnut and Acyclovir. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Horse Chestnut and Acyclovir have any of the same side effects?
Yes — our sources link each of them separately to 6 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Horse Chestnut and Acyclovir combination checked?
Interactions in our licensed database are recorded against drug classes. Acyclovir is filed under 6 classifications, and Horse Chestnut has documented interactions with 1 drug class — none of Acyclovir's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Horse Chestnut interact with any other medications?
Yes. Horse Chestnut has 122 documented drug interactions in our database — Acyclovir is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Acyclovir interact with any supplements?
Yes. Acyclovir has documented interactions with 37 supplements in our database — Horse Chestnut is not one of them. The Acyclovir interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Horse Chestnut monograph Uses, safety profile, and every drug interaction in one place Acyclovir drug information The full plain-English guide to this medication Acyclovir supplement interactions Every supplement checked against Acyclovir, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 21 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Acyclovir and Horse Chestnut?

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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.