Drug & supplement interaction

Horsetail + Zidovudine

Zidovudine brand names: Retrovir, Retrovir Injection.

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

Horsetail has a moderate interaction with Zidovudine. 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?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Horsetail and Zidovudine

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

Moderate

NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NRTIs)

Why this applies to Zidovudine

Zidovudine 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 concern with pairing horsetail and your HIV medicine zidovudine (Retrovir). The worry isn't that zidovudine becomes too strong, it's the opposite: there's a chance horsetail could make this medicine work less well. Since zidovudine helps keep the amount of HIV in your blood low, anything that weakens it could let your viral load creep back up, which is exactly what you don't want.

I want to be honest about how solid this is. It comes from just two case reports where people on HIV regimens (one including zidovudine) had detectable virus while taking horsetail, and the levels dropped again after they stopped it. Nobody knows the actual mechanism, so this is fairly weak, theoretical evidence. Still, with HIV therapy I'd rather you not gamble. Please check with your pharmacist or HIV doctor before using any horsetail product.

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 Zidovudine 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. Zidovudine)
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 Zidovudine

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 Zidovudine, 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 Zidovudine

This page covers Horsetail only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Zidovudine page lists 60 supplements it has a documented interaction with, worst first, each one explained.

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

By severity: 4 major · 47 moderate · 9 minor.

From our pharmacist’s overview on the Zidovudine page

“The liver is where the biggest danger on this page sits. Zidovudine (Retrovir), an HIV medicine that can strain the liver on its own, has 38 listed ingredients capable of piling on additional liver stress, led by Siberian cocklebur, a major-rated entry linked to actual liver failure.”

Reviewed by 2 · Jul 18, 2026

Open the Zidovudine 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 Zidovudine 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 Zidovudine 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 Zidovudine
Steady interest

#2,642 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 Zidovudine

What Is Zidovudine Used For?

Brand names: Retrovir, Retrovir Injection

Zidovudine is used in combination with other antiretroviral medicines to treat HIV-1 infection in adults and children. It is available as capsules, tablets, oral solution, and — as Retrovir injection — intravenously for patients who cannot take oral forms.

Retrovir (zidovudine) capsules, oral solution, and injection are also approved to help prevent HIV-1 from passing from a pregnant mother to her baby. This prevention regimen involves treating the mother before and during labor, and then treating the newborn after birth. In most cases, other antiretroviral medicines are used alongside zidovudine for this purpose.

See full Zidovudine 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 Zidovudine, 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 Zidovudine supplement interactions › Every supplement checked against Zidovudine, ranked by severity Zidovudine 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 Zidovudine Together: Common Questions

Can you take Horsetail with Zidovudine?
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 Zidovudine 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 Zidovudine and Horsetail?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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.