Drug & supplement interaction

Schizonepeta + Dextromethorphan HBr, Guaifenesin

Dextromethorphan HBr, Guaifenesin brand names: Vicks Formula 44E Cough & Chest Congestion Relief, Pediatric Vicks Formula 44e Cough & Chest Congesti.

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

Dextromethorphan HBr, Guaifenesin falls into 2 drug categories that Schizonepeta can interact with; the most serious is rated moderate. Animal research suggests that schizonepetin, a monoterpene constituent of schizonepeta, inhibits cytochrome P450 (CYP) 2D6.

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

Schizonepeta and Dextromethorphan HBr, Guaifenesin

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

Why Are There 2 Interactions?

Schizonepeta interacts with whole categories of medication. Dextromethorphan HBr, Guaifenesin falls into 2 of those categories, so it can interact with Schizonepeta 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 2D6 (CYP2D6) SUBSTRATES

1 of 2

Why this applies to Dextromethorphan HBr, Guaifenesin

Dextromethorphan HBr, Guaifenesin falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES — the group Schizonepeta interacts with.

Animal research suggests that schizonepetin, a monoterpene constituent of schizonepeta, inhibits cytochrome P450 (CYP) 2D6. Theoretically, schizonepeta might increase the effects and side effects of CYP2D6 substrates.
Some substrates of CYP2D6 include amitriptyline (Elavil), codeine, desipramine (Norpramin), flecainide (Tambocor), haloperidol (Haldol), imipramine (Tofranil), metoprolol (Lopressor, Toprol XL), ondansetron (Zofran), paroxetine (Paxil), risperidone (Risperdal), tramadol (Ultram), venlafaxine (Effexor), and others.
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 cough syrup: the dextromethorphan part is cleared from your body mainly by a liver enzyme called CYP2D6. Lab and animal studies hint that a compound in Schizonepeta may slow that enzyme down. If that happens, dextromethorphan could build up a bit, meaning more of its usual effects like drowsiness, dizziness, or feeling foggy. The guaifenesin (the mucus-thinner) isn't really affected.

I want to be honest, though: this is only seen in test tubes and animals, not people, so it's mostly theoretical. For most folks taking a normal dose for a few days, this likely won't cause trouble. Still, if you use Schizonepeta regularly, it's worth a quick chat with your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Bao B, Geng T, Cao Y, et al. Effects of schizonepetin on activity of mRNA expression of cytochrome P450 enzymes in rats. Int J Mol Sci. 2012;13(12):17006-18.
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

Dextromethorphan HBr, Guaifenesin also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Animal research suggests that schizonepetin, a monoterpene constituent of schizonepeta, induces cytochrome P450 (CYP) 3A4. Theoretically, schizonepeta might decrease the effects of CYP3A4 substrates.
Some substrates of CYP3A4 include lovastatin (Mevacor), ketoconazole (Nizoral), itraconazole (Sporanox), fexofenadine (Allegra), triazolam (Halcion), and numerous others.
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 cough syrup. The dextromethorphan part is partly cleared by a liver enzyme called CYP3A4. Animal studies hint that schizonepeta may speed up that enzyme. In theory, that could clear dextromethorphan a bit faster, meaning your cough suppressant might not work quite as well. The guaifenesin (the expectorant that loosens mucus) isn't really affected this way.

Honestly, this is weak, lab-and-animal-only evidence, so I wouldn't lose sleep over it. You're more likely to just notice your cough relief feeling a little underwhelming than to have anything dangerous happen. If you take schizonepeta regularly and your cough medicine seems less helpful, mention it to your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Bao B, Geng T, Cao Y, et al. Effects of schizonepetin on activity of mRNA expression of cytochrome P450 enzymes in rats. Int J Mol Sci. 2012;13(12):17006-18.

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

Schizonepeta Also Interacts With Other Medications

Schizonepeta has 796 moderate known drug interactions in our database — the Dextromethorphan HBr, Guaifenesin one above is among them. If you take anything else, check it against the full list below.

Moderate 796 No known interaction 2,034 (incl. Dextromethorphan HBr, Guaifenesin)
Taking anything else?

Check Another of Your Medications Against Schizonepeta

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

Everything else you take

See Every Supplement That Interacts With Dextromethorphan HBr, Guaifenesin

This page covers Schizonepeta only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dextromethorphan HBr, Guaifenesin page lists 171 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), Lithium (major), St. John's Wort (major) and 1,3-dmaa (moderate).

By severity: 4 major · 125 moderate · 42 minor.

From our pharmacist’s overview on the Dextromethorphan HBr, Guaifenesin page

“A bad cough tends to hit when supplements are already on the counter, and anyone reaching for Vicks Formula 44E (dextromethorphan HBr and guaifenesin) should treat this list with real care, since 4 of its 171 entries carry a major rating. Two themes dominate.”

Reviewed by 2 · Jul 18, 2026

Open the Dextromethorphan HBr, Guaifenesin interaction page

One more smart check

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

We hold 285 real supplement products containing Schizonepeta, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Schizonepeta. Your product may carry other ingredients that interact with Dextromethorphan HBr, Guaifenesin too, on top of Schizonepeta — 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 Schizonepeta and Dextromethorphan HBr, Guaifenesin 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 Schizonepeta
Top half

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

29 days ago today
Medication Dextromethorphan HBr, Guaifenesin
Top 25%

#665 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 Schizonepeta

What is Schizonepeta?

  • Common cold and early-stage fever
  • Itchy skin rashes and hives
  • Sore throat
  • Headache
  • Measles and other skin eruptions (traditional use)

Schizonepeta is a mint-family herb long used in traditional Chinese medicine, usually as part of combination formulas for colds, fevers, and itchy skin conditions. Modern human evidence is very limited, so its benefits are not well proven. Talk to a pharmacist or doctor before using it, especially if you are pregnant, breastfeeding, or taking other medicines.

Read the full Schizonepeta monograph & all interactions
Keep checking

Other Drugs & Schizonepeta

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

0Major
796Moderate
0Minor
2,033No known interaction
796 Moderate 2,033 No interaction
Moderate

796 interactions

Showing 60 of 796 moderate interactions — see all 796 on the Schizonepeta page.

No interaction 2,033 drugs checked — show the list

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

Showing the 60 most looked-up of 2,033 medications checked with no known interaction — see the full Schizonepeta list.

See the full Schizonepeta interactions page
See every supplement checked against Dextromethorphan HBr, Guaifenesin, 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
Schizonepeta monograph › Uses, safety, and every drug interaction in one place Dextromethorphan HBr, Guaifenesin supplement interactions › Every supplement checked against Dextromethorphan HBr, Guaifenesin, 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 Schizonepeta and Dextromethorphan HBr, Guaifenesin Together: Common Questions

Can you take Schizonepeta with Dextromethorphan HBr, Guaifenesin?
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 Schizonepeta and Dextromethorphan HBr, Guaifenesin?
Dextromethorphan HBr, Guaifenesin belongs to more than one drug category, and Schizonepeta 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 Schizonepeta and Dextromethorphan HBr, Guaifenesin 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 Dextromethorphan HBr, Guaifenesin and Schizonepeta?

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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.