Drug & supplement interaction

Red Clover + Tamoxifen Citrate

Tamoxifen Citrate brand names: Nolvadex, Soltamox.

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

Tamoxifen Citrate falls into 3 drug categories that Red Clover can interact with; the most serious is rated moderate. Theoretically, the phytoestrogens in red clover might interfere with tamoxifen.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Red Clover and Tamoxifen Citrate

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Red Clover interacts with whole categories of medication. Tamoxifen Citrate falls into 3 of those categories, so it can interact with Red Clover in 3 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

TAMOXIFEN (Nolvadex)

1 of 3
Theoretically, the phytoestrogens in red clover might interfere with tamoxifen.
In vitro and animal research suggests that genistein, a constituent of red clover, might antagonize the antitumor effects of tamoxifen. However, there is some evidence from an animal study that red clover does not reduce the efficacy of tamoxifen. Until more is known, tell patients taking tamoxifen to avoid red clover.
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 red clover and tamoxifen. Tamoxifen works by blocking estrogen from reaching breast cancer cells. Red clover is packed with isoflavones (plant compounds that act a little like estrogen). On paper, those plant estrogens could push against what tamoxifen is trying to do, possibly making it work less well. That matters a lot when a medicine is helping treat or prevent breast cancer.

Now, the honest part: this worry is mostly theoretical, based on lab dishes and animal studies, and one animal study didn't show a problem. We just don't have solid human proof either way. Because the stakes are so high, most experts say play it safe and skip red clover supplements here. Please don't change anything on your own. Talk with your pharmacist or oncologist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. This P, De La Rochefordiere A, Clough K, et al. Phytoestrogens after breast cancer. Endocr Relat Cancer 2001;8:129-34. PubMed
  2. Ferraris C, Ballestra B, Listorti C, et al. Red clover and lifestyle changes to contrast menopausal symptoms in premenopausal patients with hormone-sensitive breast cancer receiving tamoxifen. Breast Cancer Res Treat 2020;180(1):157-65. doi: 10.1007/s1054 PubMed
Minor

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

2 of 3

Why this applies to Tamoxifen Citrate

Tamoxifen Citrate falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES — the group Red Clover interacts with.

Theoretically, red clover might increase levels of drugs metabolized by CYP2C9; however, a small clinical study found no effect.
In vitro evidence suggests that red clover might inhibit CYP2C9. However, a clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of tolbutamide, a CYP2C9 probe substrate.
Severity Minor Likelihood Unlikely Evidence D

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 short version on combining red clover with tamoxifen. In lab dish studies, red clover's isoflavones looked like they might slow down CYP2C9, one of the liver enzymes that helps process tamoxifen. In theory, slowing that enzyme could let a bit more drug build up. But this is weak, test-tube level evidence, and a small human study using standardized red clover (60 mg isoflavones twice daily) showed no real change in how a CYP2C9 drug was handled. So a meaningful interaction here is considered unlikely.

My bigger caution is different: red clover acts like a weak plant estrogen, and tamoxifen works by blocking estrogen's effect on breast tissue. Because of that overlap, please check with your oncologist or pharmacist before using red clover.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Commun Mass Spectrom 2004;1 PubMed
  2. Chen L, Choi J, Leonard SW, et al. No Clinically Relevant Pharmacokinetic Interactions of a Red Clover Dietary Supplement with Cytochrome P450 Enzymes in Women. J Agric Food Chem. 2020;68(47):13929-13939. PubMed
Minor

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

3 of 3

Tamoxifen Citrate also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, red clover might increase levels of drugs metabolized by CYP3A4; however, a small clinical study found no effect.
In vitro evidence shows that red clover might inhibit CYP3A4 isoenzymes. However, a clinical study in healthy postmenopausal individuals shows that taking red clover capsules standardized to contain 60 mg isoflavones twice daily for 14 days does not affect the pharmacokinetics of alprazolam, a CYP3A4 probe substrate.
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 bigger picture with red clover and tamoxifen. On paper, red clover's isoflavones might slow down CYP3A4, one of the liver enzymes that helps process tamoxifen. If that happened, tamoxifen levels could nudge up a little. But a small human study found red clover capsules didn't actually change how the body handled a similar CYP3A4 drug, so this enzyme concern looks unlikely to matter in real life.

The thing I'd flag more is that red clover acts like a weak plant estrogen. Tamoxifen works by blocking estrogen in breast tissue, so adding an estrogen-like supplement could theoretically work against your treatment. The evidence here is weak, but because this medicine guards against breast cancer, please check with your oncologist or pharmacist before starting red clover.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Budzinski JW, Foster BC, Vandenhoek S, Arnason JT. An in vitro evaluation of human cytochrome P450 3A4 inhibition by selected commercial herbal extracts and tinctures. Phytomedicine 2000;7:273-82. PubMed
  2. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Commun Mass Spectrom 2004;1 PubMed
  3. Chen L, Choi J, Leonard SW, et al. No Clinically Relevant Pharmacokinetic Interactions of a Red Clover Dietary Supplement with Cytochrome P450 Enzymes in Women. J Agric Food Chem. 2020;68(47):13929-13939. 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

Red Clover Also Interacts With Other Medications

Red Clover has 43 moderate, 823 minor known drug interactions in our database — the Tamoxifen Citrate one above is among them. If you take anything else, check it against the full list below.

Moderate 43 Minor 823 No known interaction 1,964 (incl. Tamoxifen Citrate)
Taking anything else?

Check Another of Your Medications Against Red Clover

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

From our Q&A

Questions About Red Clover or Tamoxifen Citrate

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

This page covers Red Clover only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Tamoxifen Citrate page lists 210 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Beer (major) and Cesium (major).

By severity: 11 major · 166 moderate · 33 minor.

From our pharmacist’s overview on the Tamoxifen Citrate page

“Tamoxifen (Nolvadex, Soltamox) often stands between a breast cancer patient and a recurrence, so the stakes on this page run higher than usual. Eleven of the 210 supplements and herbs on file carry a major rating, and those eleven deserve your attention ahead of everything else.”

Reviewed by 2 · Jul 18, 2026

Open the Tamoxifen Citrate interaction page

One more smart check

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

We hold 1,480 real supplement products containing Red Clover, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Red Clover. Your product may carry other ingredients that interact with Tamoxifen Citrate too, on top of Red Clover — 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 Red Clover and Tamoxifen Citrate 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 Red Clover
Top 25%

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

29 days ago today
Medication Tamoxifen Citrate
Top 25%

#399 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 Red Clover

What is Red Clover?

Red Clover
  • Menopause symptoms (hot flashes)
  • High cholesterol
  • Bone health/osteoporosis
  • Skin and hair concerns
  • Women's health

Red clover is a plant rich in isoflavones (plant compounds with weak estrogen-like activity) that is most often used for menopause symptoms like hot flashes. The evidence is mixed and generally weak, with some studies showing modest benefit and others showing none. Because of its hormone-like effects, it's not for everyone—talk with your pharmacist or doctor before trying it, especially if you have a hormone-sensitive condition.

Read the full Red Clover monograph & all interactions
Medication

About Tamoxifen

What Is Tamoxifen Used For?

Brand names: Nolvadex, Soltamox

Tamoxifen is used to treat estrogen receptor-positive metastatic breast cancer in both women and men, and as follow-up (adjuvant) therapy after surgery for early-stage breast cancer in women. It also reduces the occurrence of cancer in the opposite breast when used as adjuvant therapy.

In women with ductal carcinoma in situ (DCIS — an early, non-invasive breast change) following surgery and radiation, tamoxifen lowers the risk of developing invasive breast cancer. It is also approved to reduce the risk of breast cancer in women who are at high risk but have not yet been diagnosed. Both Tamoxifen Citrate tablets and Soltamox oral solution share these indications.

See full Tamoxifen drug information
Keep checking

Other Drugs & Red Clover

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

0Major
43Moderate
823Minor
1,963No known interaction
43 Moderate 823 Minor 1,963 No interaction
Moderate

43 interactions

Minor

823 interactions

Showing 60 of 823 minor interactions — see all 823 on the Red Clover page.

No interaction 1,963 drugs checked — show the list

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

Showing the 60 most looked-up of 1,963 medications checked with no known interaction — see the full Red Clover list.

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

Can you take Red Clover with Tamoxifen Citrate?
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 3 interactions listed for Red Clover and Tamoxifen Citrate?
Tamoxifen Citrate belongs to more than one drug category, and Red Clover 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 Red Clover and Tamoxifen Citrate 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 Tamoxifen Citrate and Red Clover?

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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.