Drug & supplement interaction

Oregon Grape + Pseudoephedrine, Terfenadine

Pseudoephedrine, Terfenadine brand name: Teldafen.

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

Oregon Grape has a moderate interaction with Pseudoephedrine, Terfenadine. Theoretically, Oregon grape might increase serum levels of drugs that are P-glycoprotein (P-gp) substrates.

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

Oregon Grape and Pseudoephedrine, Terfenadine

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

Moderate

P-GLYCOPROTEIN SUBSTRATES

Why this applies to Pseudoephedrine, Terfenadine

Pseudoephedrine, Terfenadine falls under P-GLYCOPROTEIN SUBSTRATES — the group Oregon Grape interacts with.

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 basic idea with this combo. Terfenadine relies on a transporter called P-glycoprotein (P-gp), which acts like a bouncer pushing the drug back out of your cells. Lab studies hint that the berberine in Oregon grape may block that bouncer, so in theory more terfenadine could build up in your blood. That matters because terfenadine is the old antihistamine that was actually pulled from the market for raising the risk of dangerous heart rhythm changes when its levels climbed too high.

I'll be honest: this is only a theoretical concern based on test-tube work, not real patient cases, so don't panic. The pseudoephedrine side could add jitteriness or a faster heartbeat too. Please check with your pharmacist or doctor before pairing these.

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 Pseudoephedrine, Terfenadine one above is one of them. If you take anything else, check it against the full list below.

Moderate 1,217 No known interaction 1,613 (incl. Pseudoephedrine, Terfenadine)
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 Pseudoephedrine, Terfenadine

This page covers Oregon Grape only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Pseudoephedrine, Terfenadine page lists 105 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), Cesium (major) and Ephedra (major).

By severity: 10 major · 77 moderate · 18 minor.

From our pharmacist’s overview on the Pseudoephedrine, Terfenadine page

“Teldafen pairs the decongestant pseudoephedrine with terfenadine, an older antihistamine known for disturbing heart rhythm, so I read this list with real seriousness and you should too. The riskiest entries either stretch the heart's QT interval further, which is how dangerous arrhythmias begin (grapefruit in large amounts is one), or…”

Reviewed by 2 · Jul 18, 2026

Open the Pseudoephedrine, Terfenadine 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 Pseudoephedrine, Terfenadine 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 Pseudoephedrine, Terfenadine 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%

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

29 days ago today
Medication Pseudoephedrine, Terfenadine
Steady interest

#1,687 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 Pseudoephedrine, Terfenadine, 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 Pseudoephedrine, Terfenadine supplement interactions › Every supplement checked against Pseudoephedrine, Terfenadine, 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 Pseudoephedrine, Terfenadine Together: Common Questions

Can you take Oregon Grape with Pseudoephedrine, Terfenadine?
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 Oregon Grape and Pseudoephedrine, Terfenadine 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 Pseudoephedrine, Terfenadine 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.