Drug & supplement interaction

Boxwood + Chlorpheniramine, Pheylephrine, Pyrilamine

Chlorpheniramine, Pheylephrine, Pyrilamine brand name: Phena-Plus.

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

Boxwood has a moderate interaction with Chlorpheniramine, Pheylephrine, Pyrilamine. Evidence from in vitro research suggests that boxwood extract can inhibit acetylcholinesterase activity.

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

Boxwood and Chlorpheniramine, Pheylephrine, Pyrilamine

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

Moderate

ANTICHOLINERGIC DRUGS

Why this applies to Chlorpheniramine, Pheylephrine, Pyrilamine

Chlorpheniramine, Pheylephrine, Pyrilamine falls under ANTICHOLINERGIC DRUGS — the group Boxwood interacts with.

Evidence from in vitro research suggests that boxwood extract can inhibit acetylcholinesterase activity. Theoretically, concurrent use of anticholinergic drugs and boxwood might decrease the effectiveness of boxwood or the anticholinergic agent.
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 Phena-Plus, which contains chlorpheniramine and pyrilamine (two antihistamines that work in part by blocking acetylcholine), plus phenylephrine (a decongestant). In lab dishes, boxwood extract appears to block an enzyme called acetylcholinesterase, which raises acetylcholine levels. Since your antihistamines work by doing the opposite, the two could theoretically tug against each other and blunt one another's effects.

I want to be honest with you though: this is only test-tube and animal data, so it's a theoretical concern, not something proven in people. Realistically you might notice slightly less relief, or a bit more dry mouth, drowsiness, or jitteriness from the mix. Boxwood also has real toxicity concerns on its own, so please check with your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Orhan, I., Sener, B., Choudhary, M. I., and Khalid, A. Acetylcholinesterase and butyrylcholinesterase inhibitory activity of some Turkish medicinal plants. J Ethnopharmacol 2004;91(1):57-60. 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

Boxwood Also Interacts With Other Medications

Boxwood has 218 moderate known drug interactions in our database — the Chlorpheniramine, Pheylephrine, Pyrilamine one above is one of them. If you take anything else, check it against the full list below.

Moderate 218 No known interaction 2,612 (incl. Chlorpheniramine, Pheylephrine, Pyrilamine)
Taking anything else?

Check Another of Your Medications Against Boxwood

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

Everything else you take

See Every Supplement That Interacts With Chlorpheniramine, Pheylephrine, Pyrilamine

This page covers Boxwood only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Chlorpheniramine, Pheylephrine, Pyrilamine page lists 198 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), Henbane (major), Lithium (major) and Scopolia (major).

By severity: 6 major · 149 moderate · 43 minor.

From our pharmacist’s overview on the Chlorpheniramine, Pheylephrine, Pyrilamine page

“Reaching for Phena-Plus (chlorpheniramine, phenylephrine, and pyrilamine) usually means a miserable cold or allergy flare, and the same cabinet often holds grapefruit juice or St. John's wort.”

Reviewed by 2 · Jul 18, 2026

Open the Chlorpheniramine, Pheylephrine, Pyrilamine interaction page

One more smart check

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

We hold 7 real supplement products containing Boxwood, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Boxwood. Your product may carry other ingredients that interact with Chlorpheniramine, Pheylephrine, Pyrilamine too, on top of Boxwood — 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 Boxwood and Chlorpheniramine, Pheylephrine, Pyrilamine 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 Boxwood
Steady interest

#1,440 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Chlorpheniramine, Pheylephrine, Pyrilamine
Top 25%

#466 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 Boxwood

What is Boxwood?

Boxwood
  • HIV/immune support
  • Malaria
  • Arthritis
  • Diabetes
  • Skin conditions
  • Fever

Boxwood is an evergreen shrub whose leaves have been used in folk medicine, most notably in some early studies looking at HIV. The whole plant is toxic, so only processed extracts are used, and solid evidence for any health benefit is very limited. Because of real safety concerns, talk with a pharmacist or doctor before trying boxwood.

Read the full Boxwood monograph & all interactions
Keep checking

Other Drugs & Boxwood

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

0Major
218Moderate
0Minor
2,611No known interaction
218 Moderate 2,611 No interaction
Moderate

218 interactions

Showing 60 of 218 moderate interactions — see all 218 on the Boxwood page.

No interaction 2,611 drugs checked — show the list

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

Showing the 60 most looked-up of 2,611 medications checked with no known interaction — see the full Boxwood list.

See the full Boxwood interactions page
See every supplement checked against Chlorpheniramine, Pheylephrine, Pyrilamine, 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
Boxwood monograph › Uses, safety, and every drug interaction in one place Chlorpheniramine, Pheylephrine, Pyrilamine supplement interactions › Every supplement checked against Chlorpheniramine, Pheylephrine, Pyrilamine, 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 Boxwood and Chlorpheniramine, Pheylephrine, Pyrilamine Together: Common Questions

Can you take Boxwood with Chlorpheniramine, Pheylephrine, Pyrilamine?
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 Boxwood and Chlorpheniramine, Pheylephrine, Pyrilamine 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 Chlorpheniramine, Pheylephrine, Pyrilamine and Boxwood?

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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.