Drug & supplement interaction

Coltsfoot + 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 Coltsfoot 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

Coltsfoot 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 Coltsfoot 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.

Coltsfoot safety at a glance

Coltsfoot overall Use caution May contain liver-toxic pyrrolizidine alkaloids; use only certified PA-free products, if at all.
Pregnancy Likely Unsafe When products containing hepatotoxic pyrrolizidine alkaloid (PA) constituents are used orally. Coltsfoot preparations containing hepatotoxic pyrrolizidine alkal... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally. Hepatotoxic pyrrolizidine alkaloid (PA) constituents in coltsfoot are excreted in milk. There is insufficient reliable information available a... 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 Coltsfoot? 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. Coltsfoot has documented interactions with 3 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), antihypertensive drugs (moderate) and cytochrome p450 3a4 (cyp3a4) inducers (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

Coltsfoot Does Interact With Other Medications

Coltsfoot has 374 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 374 No known interaction 2,456 (incl. Acyclovir)
Taking anything else?

Check Another of Your Medications Against Coltsfoot

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

What to actually watch for

No Interaction Found — But Data Suggests Coltsfoot and Acyclovir May Share a Side Effect

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.

  • Vomiting Additional detail

    Coltsfoot

    “Orally, the major concern with coltsfoot use is its pyrrolizidine alkaloid (PA) content. These alkaloids can cause liver and lung injury. Chronic exposure to other plants containing hepatotoxic PA constituents has been associated with hepatic veno-occlusive disease. Sub-acute veno-occlusive disease can cause vague symptoms, including colicky pains, vomiting, diarrhea, and ascites within several days;”

    Coltsfoot · Natural Medicines adverse-effect record, reported in diarrhea.

    4 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
    3. 4021. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
    4. 18242. Freshour JE, Odle B, Rikhye S, Stewart DW. Coltsfoot as a potential cause of deep vein thrombosis and pulmonary embolism in a patient also consuming kava and blue vervain. J Diet Suppl 2012;9:149-54. PubMed

    “Orally, coltsfoot might cause liver damage. Coltsfoot contains hepatotoxic pyrrolizidine alkaloids (PAs). Chronic exposure to other plants containing hepatotoxic PAs is associated with veno-occlusive disease. Sub-acute veno-occlusive disease can cause vague symptoms, including colicky pains, vomiting, diarrhea, and ascites within several days; persistent liver enlargement occurs within a few weeks.”

    Coltsfoot · Natural Medicines adverse-effect record, reported in diarrhea.

    3 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
    3. 4021. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.

    Acyclovir

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

Reported for Coltsfoot but not commonly for Acyclovir: blood clots, raised blood pressure, liver problems and diarrhea.

Effects for Acyclovir come from the ADVERSE REACTIONS section of its FDA label; effects for Coltsfoot 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

Coltsfoot in Pregnancy & Breastfeeding

Pregnancy Likely Unsafe

When products containing hepatotoxic pyrrolizidine alkaloid (PA) constituents are used orally. Coltsfoot preparations containing hepatotoxic pyrrolizidine alkaloid (PA) constituents might be teratogenic and hepatotoxic. There is one case report of fatal hepatic veno-occlusive disease in a neonate associated with regular maternal consumption during pregnancy of an herb tea containing several pyrrolizidine alkaloid herbs, including coltsfoot. There is insufficient reliable information available about the safety of using coltsfoot products certified and labeled as hepatotoxic PA-free during pregnancy; avoid using.

Lactation Likely Unsafe

When used orally. Hepatotoxic pyrrolizidine alkaloid (PA) constituents in coltsfoot are excreted in milk. There is insufficient reliable information available about the safety of using coltsfoot products certified and labeled as hepatotoxic PA-free during 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 Coltsfoot 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 Coltsfoot 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 Coltsfoot 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 Coltsfoot as Part of a Dietary Supplement Product? Check It for Interactions

We hold 60 real supplement products containing Coltsfoot, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Coltsfoot. Even though Coltsfoot 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 Coltsfoot 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 Coltsfoot
Steady interest

#1,104 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 Coltsfoot reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Coltsfoot and Acyclovir records this page draws on were last updated July 11, 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 Coltsfoot

What is Coltsfoot?

Coltsfoot
  • Cough
  • Sore throat
  • Bronchitis and congestion
  • Loosening mucus (expectorant)
  • Asthma symptoms

Coltsfoot is a traditional herb long used to soothe coughs and clear mucus, but solid human evidence for these uses is lacking. More importantly, the raw plant can contain liver-toxic pyrrolizidine alkaloids, so it carries real safety concerns and is best avoided unless you use a product certified to be free of these compounds.

Tussilago farfara · Asteraceae · Leaves and flowers · Tea, dried herb, tincture, syrup, capsules, lozenges

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

Coltsfoot: dosing

There is no established, standardized dose for coltsfoot, and because of the safety concerns, no dose can be considered clearly safe. Traditional products include teas, syrups, and tinctures, but the amount of active and toxic compounds can vary widely between products.If you choose to use coltsfoot despite the risks, only use a product certified to be free of pyrrolizidine alkaloids, follow the label directions exactly, and use it for the shortest time possible.

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

Read the full Coltsfoot 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 & Coltsfoot

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

0Major
374Moderate
0Minor
2,455No known interaction
374 Moderate 2,455 No interaction
Moderate

374 interactions

Showing 60 of 374 moderate interactions — see all 374 on the Coltsfoot page.

No interaction 2,455 drugs checked — show the list

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

Showing the 60 most looked-up of 2,455 medications checked with no known interaction — see the full Coltsfoot list.

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

Coltsfoot References

The 8 references that drive our Coltsfoot 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. Roulet M, Laurini R, Rivier L, Calame A. Hepatic veno-occlusive disease in newborn infant of a woman drinking herbal tea. J Pediatr 1988;112:433-6. PubMed
  2. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
  3. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  4. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
  5. Wilson BE, Hobbs WN. Case report: pseudoephedrine-associated thyroid storm: thyroid hormone-catecholamine interactions. Am J Med Sci 1993;306:317-9. PubMed
  6. Wang YP, Yan J, Fu PP, Chou MW. Human liver microsomal reduction of pyrrolizidine alkaloid N-oxides to form the corresponding carcinogenic parent alkaloid. Toxicol Lett 2005;155:411-20. PubMed
  7. Hwang SB, Chang MN, Garcia ML, et al. L-652,469--a dual receptor antagonist of platelet activating factor and dihydropyridines from Tussilago farfara L. Eur J Pharmacol 1987;141:269-81. PubMed
  8. Freshour JE, Odle B, Rikhye S, Stewart DW. Coltsfoot as a potential cause of deep vein thrombosis and pulmonary embolism in a patient also consuming kava and blue vervain. J Diet Suppl 2012;9:149-54. 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 Coltsfoot and Acyclovir Together: Common Questions

Is it safe to take Coltsfoot with Acyclovir?
We do not list a known interaction between Coltsfoot 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 Coltsfoot and Acyclovir have any of the same side effects?
Yes — our sources link each of them separately to one 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 Coltsfoot and Acyclovir combination checked?
Interactions in our licensed database are recorded against drug classes. Acyclovir is filed under 6 classifications, and Coltsfoot has documented interactions with 3 drug classes — 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 Coltsfoot interact with any other medications?
Yes. Coltsfoot has 374 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 — Coltsfoot 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

Coltsfoot 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 8 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Acyclovir and Coltsfoot?

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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.