Drug & supplement interaction

Horsetail + Adefovir

Adefovir brand name: Hepsera.

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

Horsetail has a moderate interaction with Adefovir. Theoretically, horsetail might decrease the levels and clinical effects of NRTIs.

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

Horsetail and Adefovir

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

Moderate

NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NRTIs)

Why this applies to Adefovir

Adefovir falls under NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NRTIs) — the group Horsetail interacts with.

Theoretically, horsetail might decrease the levels and clinical effects of NRTIs.
In two case reports, patients were found to have detectable viral loads when taking horsetail-containing supplements along with an antiretroviral therapy. In one case, the antiretroviral regimen included zidovudine, lamivudine, and efavirenz; in the other case, the regimen consisted of emtricitabine, tenofovir disoproxil fumarate, and efavirenz. One month after discontinuing the supplement, the viral loads became undetectable in both cases. The exact mechanism of these interactions is unknown. It is also unclear if these interactions are specific to NRTIs or if they are related to various components of antiretroviral therapy.
Severity Moderate Likelihood Possible Evidence D

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 honest picture: we don't have solid proof that horsetail interferes with adefovir (Hepsera) specifically. The concern comes from just two case reports in people on HIV regimens, where their virus became detectable while taking horsetail and then dropped back to undetectable a month after they stopped. Nobody knows the exact reason, and adefovir wasn't one of the drugs involved.

Still, the worry is the same direction for any antiviral like this: horsetail might lower the drug's effect, which could let your hepatitis B virus levels creep back up and make the treatment work less well. That's why I'd suggest checking with your doctor or pharmacist before pairing them, especially since horsetail can also drain your vitamin B1 over time.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Cordova E, Morganti L, Rodriguez C. Possible Drug-Herb Interaction between Herbal Supplement Containing Horsetail (Equisetum arvense) and Antiretroviral Drugs. J Int Assoc Provid AIDS Care. 2017;16(1):11-13.

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

Horsetail Also Interacts With Other Medications

Horsetail has 187 moderate known drug interactions in our database — the Adefovir one above is one of them. If you take anything else, check it against the full list below.

Moderate 187 No known interaction 2,643 (incl. Adefovir)
Taking anything else?

Check Another of Your Medications Against Horsetail

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

From our Q&A

Questions About Horsetail or Adefovir

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

This page covers Horsetail only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Adefovir page lists 28 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 · 15 moderate · 10 minor.

From our pharmacist’s overview on the Adefovir page

“Someone taking adefovir (Hepsera) for hepatitis B is asking a lot of their kidneys already, since the drug can stress them, and that is where the riskiest entries here press. Six of these 28 ingredients, Siberian cocklebur most seriously, can harm the kidneys themselves, and four more block the transporter the kidneys use to clear adef…”

Reviewed by 2 · Jul 18, 2026

Open the Adefovir interaction page

One more smart check

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

We hold 2,089 real supplement products containing Horsetail, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Horsetail. Your product may carry other ingredients that interact with Adefovir too, on top of Horsetail — 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 Horsetail and Adefovir 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 Horsetail
Top 10%

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

29 days ago today
Medication Adefovir
Steady interest

#1,672 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 Horsetail

What is Horsetail?

Horsetail
  • Fluid retention (mild diuretic)
  • Urinary and bladder concerns
  • Hair, skin, and nail support
  • Wound healing
  • Bone health

Horsetail is a traditional herb most often used as a mild diuretic and for hair, nail, and bone support, but high-quality human evidence is limited. It can cause thiamine (vitamin B1) loss with long-term use, and some related species are toxic, so choose products carefully and talk to your pharmacist or doctor before using it.

Read the full Horsetail monograph & all interactions
Medication

About Adefovir

What Is Adefovir Used For?

Brand name: Hepsera

Adefovir Dipivoxil Tablets and Hepsera are used to treat chronic hepatitis B — a long-term liver infection caused by the hepatitis B virus (HBV) — in patients 12 years of age and older who have signs of active viral replication and either persistently elevated liver enzymes or active liver disease confirmed on biopsy.

The indication covers adults with both HBeAg-positive and HBeAg-negative chronic hepatitis B, including those with lamivudine-resistant hepatitis B virus. In adolescents aged 12 to less than 18, the approval is based on virological and biochemical responses in HBeAg-positive patients with compensated (still-functioning) liver disease.

See full Adefovir drug information
Keep checking

Other Drugs & Horsetail

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

0Major
187Moderate
0Minor
2,642No known interaction
187 Moderate 2,642 No interaction
Moderate

187 interactions

Showing 60 of 187 moderate interactions — see all 187 on the Horsetail page.

No interaction 2,642 drugs checked — show the list

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

Showing the 60 most looked-up of 2,642 medications checked with no known interaction — see the full Horsetail list.

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

Can you take Horsetail with Adefovir?
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 Horsetail and Adefovir 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 Adefovir and Horsetail?

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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.