Drug & supplement interaction

Cardarine + Letrozole

Letrozole brand name: Femara.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Cardarine and Letrozole 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.

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Interaction report

Cardarine and Letrozole

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 Letrozole and Cardarine 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.

Worth understanding: our licensed dataset holds no drug-interaction record for Cardarine at all — not against Letrozole, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

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.

Cardarine safety at a glance

Cardarine overall Avoid Animal studies linked it to cancer and it is not approved or proven safe for human use.
Pregnancy Possibly Unsafe When used orally or parenterally. Some metabolic modulators have been found to cause cancer in animals. Their safety in humans has not been tested. Avoid using. Read the full pregnancy detail
Breastfeeding Possibly Unsafe When used orally or parenterally. Some metabolic modulators have been found to cause cancer in animals. Their safety in humans has not been tested. Avoid using. 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 Letrozole and Cardarine? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Letrozole’s Own FDA Label Lists

This is not an interaction — none of it involves Cardarine. These are the most notable effects listed in the ADVERSE REACTIONS section of Letrozole’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. One of them is worth acting on rather than waiting out — marked below.

  • Bleeding or bruising Worth acting on
  • Flushing
  • Sweating
  • Joint pain
  • Muscle pain
  • Swelling
  • Tiredness
  • Dizziness
  • Headache
  • Nausea

From the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed › Cardarine’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Cardarine side to compare — that is a limit of the record, not a statement that Cardarine has no side effects.

Special populations

Cardarine in Pregnancy & Breastfeeding

Pregnancy And Lactation Possibly Unsafe

When used orally or parenterally. Some metabolic modulators have been found to cause cancer in animals. Their safety in humans has not been tested. 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 Cardarine or Letrozole

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

This page covers Cardarine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

One more smart check

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

We hold 18 real supplement products containing Cardarine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Cardarine. Even though Cardarine itself has no known interaction with Letrozole, 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 Cardarine and Letrozole 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 Cardarine
Steady interest

#1,179 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Letrozole
Top 5%

#50 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 Cardarine reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Cardarine and Letrozole records this page draws on were last updated June 22, 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 Cardarine

What is Cardarine?

  • Endurance and athletic performance
  • Fat loss and body recomposition
  • Bodybuilding cycles
  • Increasing exercise capacity

Cardarine (GW501516) is a synthetic experimental drug, not a vitamin, herb, or true dietary supplement, even though it is often sold as one. Animal studies linked it to a higher risk of cancer, drug development was halted, and it is banned in sports — so it should not be used. There is no proven safe dose for humans.

Not applicable (synthetic chemical compound) · Capsules, tablets, oral liquids, powders (sold as a 'research chemical')

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

Cardarine: dosing

There is no established safe or approved dose of Cardarine for humans. It is not approved by the FDA for any condition, and no medical or pharmacy authority endorses a dosing plan.Doses listed on websites and forums are not based on reliable safety research and should not be trusted.

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

Read the full Cardarine monograph & all interactions
Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara) is used to treat breast cancer in postmenopausal women whose tumors are driven by estrogen. It is used in three settings: as adjuvant (after-surgery) treatment for hormone receptor positive early breast cancer; as extended adjuvant treatment for women who have already completed about five years of tamoxifen therapy; and as first- or second-line treatment for locally advanced or metastatic (spread) breast cancer.

Femara is specifically indicated for first-line treatment of hormone receptor positive or receptor-unknown locally advanced or metastatic breast cancer, and for advanced breast cancer in women whose disease has progressed after antiestrogen therapy.

See full Letrozole drug information
Keep checking

Other Drugs & Cardarine

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Cardarine list.

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

Cardarine References

The 1 references that drive our Cardarine 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. What Should Tested Athletes Know About GW1516? Education, Spirit of Sport. U.S. Anti-Doping Agency (USADA). September 24, 2019. Available at: https://www.usada.org/spirit-of-sport/education/what-should-athletes-know-gw1516/

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 Cardarine and Letrozole Together: Common Questions

Is it safe to take Cardarine with Letrozole?
We do not list a known interaction between Cardarine and Letrozole. 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.
Does Letrozole interact with any supplements?
Yes. Letrozole has documented interactions with 142 supplements in our database — Cardarine is not one of them. The Letrozole 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

Cardarine monograph Uses, safety profile, and every drug interaction in one place Letrozole drug information The full plain-English guide to this medication Letrozole supplement interactions Every supplement checked against Letrozole, 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 1 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Cardarine?

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.