Drug & supplement interaction

Ostarine + 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 Ostarine 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

Ostarine 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 Ostarine 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.

Ostarine safety at a glance

Ostarine overall Avoid Ostarine is an unapproved investigational drug with documented safety risks and no FDA approval.
Pregnancy Avoid It affects hormone pathways and must be avoided during pregnancy.
Breastfeeding Avoid There is no safety data, so avoid while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Acyclovir and Ostarine? 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. Ostarine has documented interactions with 6 drug classes — the most serious being cytochrome p450 3a4 (cyp3a4) inducers (moderate), hepatotoxic drugs (moderate) and probenecid (benemid) (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

Ostarine Does Interact With Other Medications

Ostarine has 440 moderate, 171 minor 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 440 Minor 171 No known interaction 2,219 (incl. Acyclovir)
Taking anything else?

Check Another of Your Medications Against Ostarine

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

What to actually watch for

No Interaction Found — But Data Suggests Ostarine 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. One of them is worth acting on rather than waiting out — marked below.

  • A higher chance of infection Worth acting on reported in 5.0% of FDA reports for Acyclovir Additional detail

    Ostarine

    “Orally, in a 16-week study of cancer patients taking ostarine 1-3 mg daily, pneumonia occurred more frequently with ostarine than with placebo. Cough and dyspnea were also reported, but at rates slightly lower than placebo. In a 12-week study of healthy elderly patients taking ostarine 1-3 mg daily, cough occurred more frequently with ostarine than with placebo.”

    Ostarine · Natural Medicines adverse-effect record, reported in cancer.

    2 sources cited
    1. 98832. Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol 2013;14(4):335-45. PubMed
    2. 98833. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II tri

    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 ›

  • Tiredness reported in 7.0% of FDA reports for Acyclovir Additional detail

    Ostarine

    “Orally, in a 16-week study of cancer patients taking ostarine 1-3 mg daily, a transient increase in alanine aminotransferase (ALT) of 2- to 4-times the upper limit of normal occurred in 7.4% of patients taking ostarine 3 mg.”

    Ostarine · Natural Medicines adverse-effect record, reported in anorexia.

    6 sources cited
    1. 98832. Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol 2013;14(4):335-45. PubMed
    2. 98833. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II tri
    3. 94879. Warning Letter: Ironmag Labs 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582464.htm Accessed: November 1, 2017
    4. 94880. Warning Letter: Panther Sports Nutrition 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm581630.htm. Accessed: November 1, 2017
    5. 94881. Warning Letter: Infantry Labs LLC 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582685.htm. Accessed: November 1, 2017
    6. 106197. Bedi H, Hammond C, Sanders D, Yang HM, Yoshida EM. Drug-induced liver injury from enobosarm (ostarine), a selective androgen receptor modulator. ACG Case Rep J 2021;8(1):e00518. PubMed

    “Orally, in a 16-week study of cancer patients taking ostarine 1-3 mg daily, headache occurred more frequently with ostarine than with placebo. Fatigue was also commonly reported, but at a rate similar to placebo. In a 12-week study of healthy elderly patients taking ostarine 1-3 mg daily, headache occurred in 29% of patients, which was more common than with placebo.”

    Ostarine · Natural Medicines adverse-effect record, reported in cancer.

    5 sources cited
    1. 98832. Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol 2013;14(4):335-45. PubMed
    2. 98833. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II tri
    3. 94879. Warning Letter: Ironmag Labs 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582464.htm Accessed: November 1, 2017
    4. 94880. Warning Letter: Panther Sports Nutrition 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm581630.htm. Accessed: November 1, 2017
    5. 94881. Warning Letter: Infantry Labs LLC 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582685.htm. Accessed: November 1, 2017

    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 ›

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

    Ostarine

    “Orally, ostarine has been commonly reported to cause gastrointestinal adverse effects. In a 16-week study of cancer patients taking ostarine 1-3 mg daily, nausea, diarrhea, constipation, abdominal pain, and anorexia occurred in 10% or more of patients, which was more common than with placebo. Vomiting was also commonly reported, although the incidence was slightly lower than placebo.”

    Ostarine · Natural Medicines adverse-effect record, reported in anorexia.

    2 sources cited
    1. 98832. Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol 2013;14(4):335-45. PubMed
    2. 98833. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II tri

    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 ›

  • Vomiting Additional detail

    Ostarine

    Recorded for Ostarine 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 ›

  • Headache Additional detail

    Ostarine

    Recorded for Ostarine in the same Natural Medicines adverse-effect record shown under Tiredness above.

    Acyclovir

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

Reported for Ostarine but not commonly for Acyclovir: liver problems, a heart attack, a low platelet count and severe muscle breakdown.

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

From our Q&A

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

We hold 33 real supplement products containing Ostarine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Ostarine. Even though Ostarine 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 Ostarine 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 Ostarine
Steady interest

#1,283 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 Ostarine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Ostarine 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 Ostarine

What is Ostarine?

  • Muscle building
  • Athletic performance
  • Fat loss / body recomposition
  • Bodybuilding cycles

Ostarine (also called MK-2866 or enobosarm) is an experimental, unapproved drug known as a SARM (selective androgen receptor modulator), not a true dietary supplement. It is not approved by the FDA, is banned in sports, and has been linked to liver injury and other serious harms, so it is not recommended for general use.

Synthetic compound (not from a plant) · Capsules, tablets, liquids, powders sold as research chemicals or 'sports supplements'

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

Ostarine: dosing

There is no established safe or approved dose of Ostarine, because it is not an approved medicine or a legitimate dietary supplement. Doses used in research studies were given under medical supervision and do not apply to over-the-counter use.We do not recommend using Ostarine. Products sold online may not contain the dose listed on the label and may include other hidden substances.

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

Read the full Ostarine 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 & Ostarine

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

0Major
440Moderate
171Minor
2,218No known interaction
440 Moderate 171 Minor 2,218 No interaction
Moderate

440 interactions

Showing 60 of 440 moderate interactions — see all 440 on the Ostarine page.

Minor

171 interactions

Showing 60 of 171 minor interactions — see all 171 on the Ostarine page.

No interaction 2,218 drugs checked — show the list

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

Showing the 60 most looked-up of 2,218 medications checked with no known interaction — see the full Ostarine list.

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

Ostarine References

The 10 references that drive our Ostarine 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. Warning Letter: Ironmag Labs 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582464.htm Accessed: November 1, 2017
  2. Warning Letter: Panther Sports Nutrition 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm581630.htm. Accessed: November 1, 2017
  3. Warning Letter: Infantry Labs LLC 10/23/17. FDA Inspections, Compliance, Enforcement, and Criminal Investigations, October 23, 2017. https://www.fda.gov/iceci/enforcementactions/warningletters/2017/ucm582685.htm. Accessed: November 1, 2017
  4. Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol 2013;14(4):335-45. PubMed
  5. Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II tri
  6. Coss CC, Jones A, Dalton JT. Pharmacokinetic drug interactions of the selective androgen receptor modulator GTx-024 (enobosarm) with itraconazole, rifampin, probenecid, celecoxib and rosuvastatin. Invest New Drugs 2016;34(4):458-67. PubMed
  7. FDA. FDA Warns against using SARMs in body building products. October 2017. Available at: https://www.fda.gov/newsevents/newsroom/fdainbrief/ucm583021.htm.
  8. Bedi H, Hammond C, Sanders D, Yang HM, Yoshida EM. Drug-induced liver injury from enobosarm (ostarine), a selective androgen receptor modulator. ACG Case Rep J 2021;8(1):e00518. PubMed
  9. Kintz P, Gheddar L, Paradis C, et al. Peroxisome Proliferator-Activated Receptor Delta Agonist (PPAR- d) and Selective Androgen Receptor Modulator (SARM) Abuse: Clinical, Analytical and Biological Data in a Case Involving a Poisonous Combination of GW1516
  10. Weinblatt D, Roy S. Drug-Induced Liver Injury Secondary to Enobosarm: A Selective Androgen Receptor Modulator. J Med Cases 2022;13(5):244-248. 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 Ostarine and Acyclovir Together: Common Questions

Is it safe to take Ostarine with Acyclovir?
We do not list a known interaction between Ostarine 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 Ostarine 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 Ostarine and Acyclovir combination checked?
Interactions in our licensed database are recorded against drug classes. Acyclovir is filed under 6 classifications, and Ostarine has documented interactions with 6 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 Ostarine interact with any other medications?
Yes. Ostarine has 611 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 — Ostarine 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

Ostarine 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 10 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Acyclovir and Ostarine?

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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.