Drug & supplement interaction

Oregon Grape + Conjugated Estrogens, Medroxyprogesterone Acetate

Conjugated Estrogens, Medroxyprogesterone Acetate brand names: Prempro, Premplus.

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

Conjugated Estrogens, Medroxyprogesterone Acetate falls into 2 drug categories that Oregon Grape can interact with; the most serious is rated moderate. Theoretically, Oregon grape might increase serum levels of drugs metabolized by CYP3A4.

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

Oregon Grape and Conjugated Estrogens, Medroxyprogesterone Acetate

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

Why Are There 2 Interactions?

Oregon Grape interacts with whole categories of medication. Conjugated Estrogens, Medroxyprogesterone Acetate falls into 2 of those categories, so it can interact with Oregon Grape 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) SUBSTRATES

1 of 2

Why this applies to Conjugated Estrogens, Medroxyprogesterone Acetate

Conjugated Estrogens, Medroxyprogesterone Acetate falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES — the group Oregon Grape interacts with.

Theoretically, Oregon grape might increase serum levels of drugs metabolized by CYP3A4.
In vitro research and preliminary clinical evidence suggest that berberine, a constituent of Oregon grape, moderately inhibits cytochrome P450 3A4 (CYP3A4).
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 gist for anyone on Prempro or Premplus. The estrogen and progestin in this combo are cleared in part by a liver enzyme called CYP3A4. Berberine, the active compound in Oregon grape root, may modestly slow that enzyme down. In theory, that could let a bit more hormone hang around in your blood than usual, which might bump up typical estrogen-related effects like breast tenderness, bloating, nausea, headaches, or spotting.

I want to be straight with you though: this is a theoretical concern based on lab work, not solid real-world cases. Everyday food amounts aren't the worry; concentrated berberine supplements are. If you'd like to use Oregon grape regularly, just run it past your pharmacist or doctor first so they can keep an eye on things.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Wu X, Li Q, Xin H, Yu A, Zhong M. Effects of berberine on the blood concentration of cyclosporin A in renal transplanted recipients: clinical and pharmacokinetic study. Eur J Clin Pharmacol 2005;61:567-72. PubMed
  2. 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
  3. Guo, Y., Chen, Y., Tan, Z. R., Klaassen, C. D., and Zhou, H. H. Repeated administration of berberine inhibits cytochromes P450 in humans. Eur J Clin Pharmacol 2012;68(2):213-217. PubMed
  4. Hermann, R. and von, Richter O. Clinical evidence of herbal drugs as perpetrators of pharmacokinetic drug interactions. Planta Med 2012;78(13):1458-1477. PubMed
Moderate

P-GLYCOPROTEIN SUBSTRATES

2 of 2

Conjugated Estrogens, Medroxyprogesterone Acetate also falls under P-GLYCOPROTEIN SUBSTRATES.

Theoretically, Oregon grape might increase serum levels of drugs that are P-glycoprotein (P-gp) substrates.
In vitro research suggests that Oregon grape extracts inhibit P-gp efflux.
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 gist for your Prempro (the combo of conjugated estrogens and medroxyprogesterone). Oregon grape contains berberine, and in lab studies only, it appears to block a cellular pump called P-glycoprotein. That pump helps move certain medicines out of your cells. If it's slowed down, a little more of your hormone medication could theoretically stick around, which might nudge up estrogen-related effects like breast tenderness, bloating, nausea, or spotting.

I want to be honest with you though: this is based on test-tube research, not real people, so we don't truly know if it matters in everyday life. Don't stop or change anything on your own. Just give your pharmacist or doctor a heads-up before adding Oregon grape supplements, and skip it during pregnancy or breastfeeding.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Fan Y, Zhou Z, Zhang L. Effect of Oregon grape root extracts on P-glycoprotein mediated transport in in vitro cell lines. J Pharm Pharm Sci 2024;26:11927. 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

Oregon Grape Also Interacts With Other Medications

Oregon Grape has 1,217 moderate known drug interactions in our database — the Conjugated Estrogens, Medroxyprogesterone Acetate one above is among them. If you take anything else, check it against the full list below.

Moderate 1,217 No known interaction 1,613 (incl. Conjugated Estrogens, Medroxyprogesterone Acetate)
Taking anything else?

Check Another of Your Medications Against Oregon Grape

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

Everything else you take

See Every Supplement That Interacts With Conjugated Estrogens, Medroxyprogesterone Acetate

This page covers Oregon Grape only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Conjugated Estrogens, Medroxyprogesterone Acetate page lists 187 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), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 152 moderate · 32 minor.

From our pharmacist’s overview on the Conjugated Estrogens, Medroxyprogesterone Acetate page

“St. John's wort tops my list of concerns for anyone on Prempro (conjugated estrogens plus medroxyprogesterone), the combination hormone therapy for menopause symptoms.”

Reviewed by 2 · Jul 18, 2026

Open the Conjugated Estrogens, Medroxyprogesterone Acetate interaction page

One more smart check

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

We hold 740 real supplement products containing Oregon Grape, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Oregon Grape. Your product may carry other ingredients that interact with Conjugated Estrogens, Medroxyprogesterone Acetate too, on top of Oregon Grape — 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 Oregon Grape and Conjugated Estrogens, Medroxyprogesterone Acetate 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 Oregon Grape
Top 25%

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

29 days ago today
Medication Conjugated Estrogens, Medroxyprogesterone Acetate
Top half

#912 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 Oregon Grape

What is Oregon Grape?

Oregon Grape
  • Psoriasis (topical)
  • Eczema and other skin conditions
  • Digestive upset
  • Mild skin infections
  • General 'detox' or tonic use

Oregon grape is a shrub whose root contains berberine and related compounds. The strongest (though still modest) evidence is for topical creams that may slightly ease psoriasis; evidence for other uses is limited. Talk with your pharmacist or doctor before using it, and avoid it during pregnancy and breastfeeding.

Read the full Oregon Grape monograph & all interactions
Keep checking

Other Drugs & Oregon Grape

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

0Major
1,217Moderate
0Minor
1,612No known interaction
1,217 Moderate 1,612 No interaction
Moderate

1,217 interactions

Showing 60 of 1,217 moderate interactions — see all 1,217 on the Oregon Grape page.

No interaction 1,612 drugs checked — show the list

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

Showing the 60 most looked-up of 1,612 medications checked with no known interaction — see the full Oregon Grape list.

See the full Oregon Grape interactions page
See every supplement checked against Conjugated Estrogens, Medroxyprogesterone Acetate, 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
Oregon Grape monograph › Uses, safety, and every drug interaction in one place Conjugated Estrogens, Medroxyprogesterone Acetate supplement interactions › Every supplement checked against Conjugated Estrogens, Medroxyprogesterone Acetate, 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 Oregon Grape and Conjugated Estrogens, Medroxyprogesterone Acetate Together: Common Questions

Can you take Oregon Grape with Conjugated Estrogens, Medroxyprogesterone Acetate?
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 Oregon Grape and Conjugated Estrogens, Medroxyprogesterone Acetate?
Conjugated Estrogens, Medroxyprogesterone Acetate belongs to more than one drug category, and Oregon Grape 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 Oregon Grape and Conjugated Estrogens, Medroxyprogesterone Acetate 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 Conjugated Estrogens, Medroxyprogesterone Acetate and Oregon Grape?

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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.