Drug & supplement interaction

Ostarine + Fosaprepitant

Fosaprepitant brand names: Emend Injection, Focinvez.

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

Fosaprepitant falls into 2 drug categories that Ostarine can interact with; the most serious is rated moderate. Theoretically, concomitant use of ostarine with CYP3A4 inducers could decrease the clinical effects of ostarine.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Ostarine and Fosaprepitant

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Ostarine interacts with whole categories of medication. Fosaprepitant falls into 2 of those categories, so it can interact with Ostarine in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INDUCERS

1 of 2

Why this applies to Fosaprepitant

Fosaprepitant falls under CYTOCHROME P450 3A4 (CYP3A4) INDUCERS — the group Ostarine interacts with.

Theoretically, concomitant use of ostarine with CYP3A4 inducers could decrease the clinical effects of ostarine.
Ostarine is partially metabolized by CYP3A4. Clinical research shows that taking rifampin, a potent inducer of CYP3A4, reduces the maximum plasma concentration of ostarine by 23% and the area under the curve by 43%.
Severity Moderate Likelihood Possible Evidence B

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 gist for this combo. Fosaprepitant (Emend Injection) is the medicine you'd be taking for a real medical reason, usually to prevent nausea and vomiting from chemotherapy. After it's given, it converts to aprepitant, which can speed up the CYP3A4 enzyme. Ostarine happens to be broken down partly by that same enzyme.

So in theory, fosaprepitant could nudge your body into clearing Ostarine a little faster, which would weaken whatever effect you're hoping to get from the Ostarine. The evidence here is indirect and modest, drawn from a stronger inducer (rifampin), not from fosaprepitant itself. Honestly, my bigger concern is Ostarine itself: it's an unapproved SARM linked to liver injury and isn't recommended. Please talk this over with your doctor or pharmacist.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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
Minor

CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS

2 of 2

Fosaprepitant also falls under CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS.

Theoretically, concomitant use of ostarine with CYP3A4 inhibitors could increase the effects and adverse effects of ostarine, although this is unlikely to be clinically significant.
Ostarine is partially metabolized by CYP3A4. However, clinical research shows that taking itraconazole, a potent inhibitor of CYP3A4, had minimal effects on the levels of ostarine in the body.
Severity Minor Likelihood Unlikely Evidence B

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist of it: Fosaprepitant (Emend), the injection often given to prevent nausea and vomiting during chemo, gently slows down a liver enzyme called CYP3A4. Since Ostarine is partly broken down by that same enzyme, blocking it could in theory let a little more Ostarine build up in your body, which might mean stronger effects and a higher chance of its known harms like liver strain.

That said, I wouldn't lose sleep over this one. The evidence is mostly theoretical, and when researchers tested Ostarine with a much stronger CYP3A4 blocker (itraconazole), levels barely budged. The bigger concern is Ostarine itself, an unapproved SARM linked to liver injury. Please loop in your doctor or pharmacist before mixing the two.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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

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

Ostarine Also Interacts With Other Medications

Ostarine has 439 moderate, 171 minor known drug interactions in our database — the Fosaprepitant one above is among them. If you take anything else, check it against the full list below.

Moderate 439 Minor 171 No known interaction 2,220 (incl. Fosaprepitant)
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.

Everything else you take

See Every Supplement That Interacts With Fosaprepitant

This page covers Ostarine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Fosaprepitant page lists 141 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate), Adrafinil (moderate) and African Wild Potato (moderate).

By severity: 2 major · 109 moderate · 30 minor.

From our pharmacist’s overview on the Fosaprepitant page

“Fosaprepitant (Emend Injection, Focinvez) is the IV drug that keeps chemotherapy from making you sick, so anything that undercuts it costs you real comfort, and I would treat this list with genuine care before adding a supplement to it. Nearly all 141 entries hinge on one liver enzyme, CYP3A4, and the traffic runs both ways, since some…”

Reviewed by 2 · Jul 18, 2026

Open the Fosaprepitant 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. Your product may carry other ingredients that interact with Fosaprepitant too, on top of Ostarine — 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 Ostarine and Fosaprepitant 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

#1,233 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Fosaprepitant
Steady interest

#2,116 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 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.

Read the full Ostarine monograph & all interactions
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
439Moderate
171Minor
2,219No known interaction
439 Moderate 171 Minor 2,219 No interaction
Moderate

439 interactions

Showing 60 of 439 moderate interactions — see all 439 on the Ostarine page.

Minor

171 interactions

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

No interaction 2,219 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 2,219 medications checked with no known interaction — see the full Ostarine list.

See the full Ostarine interactions page
See every supplement checked against Fosaprepitant, 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
Ostarine monograph › Uses, safety, and every drug interaction in one place Fosaprepitant supplement interactions › Every supplement checked against Fosaprepitant, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Ostarine and Fosaprepitant Together: Common Questions

Can you take Ostarine with Fosaprepitant?
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.
Why are there 2 interactions listed for Ostarine and Fosaprepitant?
Fosaprepitant belongs to more than one drug category, and Ostarine interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Ostarine and Fosaprepitant 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

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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.