Drug & supplement interaction

Chrysin + Letrozole

Letrozole brand name: Femara.

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

Chrysin has a moderate interaction with Letrozole. Theoretically, chrysin might increase the effects and adverse effects of aromatase inhibitors.

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

Chrysin and Letrozole

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

Moderate

AROMATASE INHIBITORS

Why this applies to Letrozole

Letrozole falls under AROMATASE INHIBITORS — the group Chrysin interacts with.

Theoretically, chrysin might increase the effects and adverse effects of aromatase inhibitors.
In vitro research suggests that chrysin might decrease estrogen synthesis by acting as an aromatase (estrogen synthetase) inhibitor..
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 simple version. Your Letrozole already works by blocking aromatase, the enzyme that makes estrogen. Chrysin, in test-tube studies, seems to do a similar thing. So putting them together could, in theory, push in the same direction and lower estrogen even more than your Letrozole alone.

What might that look like? More of the usual Letrozole effects, things like hot flashes, joint and bone aches, fatigue, or headaches. I want to be honest though: this concern comes only from lab research, and the body absorbs very little chrysin, so we don't actually know it matters in real people. Since you're treating breast cancer, I wouldn't add chrysin without first checking with your oncologist or pharmacist.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Kao YC, Zhou C, Sherman M, et al. Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogens: A site-directed mutagenesis study. Environ Health Perspect 1998;106:85-92. PubMed
  2. Jeong HJ, Shin YG, Kim IH, Pezzuto JM. Inhibition of aromatase activity by flavonoids. Arch Pharm Res 1999;22:309-12. 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

Chrysin Also Interacts With Other Medications

Chrysin has 178 moderate, 179 minor known drug interactions in our database — the Letrozole one above is one of them. If you take anything else, check it against the full list below.

Moderate 178 Minor 179 No known interaction 2,473 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Chrysin

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

From our Q&A

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

We hold 272 real supplement products containing Chrysin, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Chrysin. Your product may carry other ingredients that interact with Letrozole too, on top of Chrysin — 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 Chrysin 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 Chrysin
Top 25%

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

29 days ago today
Medication Letrozole
Top 5%

#51 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 Chrysin

What is Chrysin?

  • Bodybuilding and testosterone support
  • Anxiety and stress
  • Anti-inflammatory
  • Antioxidant support
  • Prostate health

Chrysin is a plant flavonoid sold mainly as a bodybuilding supplement claimed to raise testosterone or block estrogen, but human studies have not shown these benefits, largely because the body absorbs very little of it. Evidence for its other proposed uses is mostly limited to laboratory and animal research, so its real-world value is unclear. Talk with your pharmacist or doctor before using it.

Read the full Chrysin 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 & Chrysin

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

0Major
178Moderate
179Minor
2,472No known interaction
178 Moderate 179 Minor 2,472 No interaction
Moderate

178 interactions

Showing 60 of 178 moderate interactions — see all 178 on the Chrysin page.

Minor

179 interactions

Showing 60 of 179 minor interactions — see all 179 on the Chrysin page.

No interaction 2,472 drugs checked — show the list

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

Showing the 60 most looked-up of 2,472 medications checked with no known interaction — see the full Chrysin list.

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

Can you take Chrysin with Letrozole?
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 Chrysin and Letrozole 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 Letrozole and Chrysin?

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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.