Drug & supplement interaction

N,n-dmpea + 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

N,n-dmpea has a moderate interaction with Dextromethorphan HBr, Guaifenesin. In vitro research shows that N,N-DMPEA strongly inhibits cytochrome P450 2D6 (CYP2D6).

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

N,n-dmpea and Dextromethorphan HBr, Guaifenesin

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

Moderate

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

Why this applies to Dextromethorphan HBr, Guaifenesin

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

In vitro research shows that N,N-DMPEA strongly inhibits cytochrome P450 2D6 (CYP2D6). Theoretically, concomitant use with drugs metabolized by CYP2D6 might increase the risk for adverse effects from these drugs.
Some drugs metabolized by CYP2D6 include amitriptyline (Elavil), clozapine (Clozaril), codeine, desipramine (Norpramin), donepezil (Aricept), fentanyl (Duragesic), flecainide (Tambocor), fluoxetine (Prozac), meperidine (Demerol), methadone (Dolophine), metoprolol (Lopressor, Toprol XL), olanzapine (Zyprexa), ondansetron (Zofran), tramadol (Ultram), trazodone (Desyrel), 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 with this combo: your body relies on an enzyme called CYP2D6 to clear dextromethorphan (the cough suppressant half of this product). N,N-DMPEA appears to block that enzyme, at least in lab studies. If it slows that breakdown, dextromethorphan can build up higher than normal, which may mean more drowsiness, dizziness, confusion, or that floaty, off-balance feeling. The guaifenesin part isn't really affected here.

The honest part: this is theoretical, based only on test-tube research, not real people. We also know very little about N,N-DMPEA itself, which is reason enough to be cautious. Since it's a stimulant-type ingredient, I'd run it by your pharmacist before pairing the two.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Liu Y, Santillo MF. Cytochrome P450 2D6 and 3A4 enzyme inhibition by amine stimulants in dietary supplements. Drug Test Anal. 2016;8(3-4):307-10. 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

N,n-dmpea Also Interacts With Other Medications

N,n-dmpea has 192 moderate known drug interactions in our database — the Dextromethorphan HBr, Guaifenesin one above is one of them. If you take anything else, check it against the full list below.

Moderate 192 No known interaction 2,638 (incl. Dextromethorphan HBr, Guaifenesin)
Taking anything else?

Check Another of Your Medications Against N,n-dmpea

Covers the 2,830 medications we’ve checked against N,n-dmpea. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Dextromethorphan HBr, Guaifenesin

This page covers N,n-dmpea 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

How much people look this up

Where N,n-dmpea 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 N,n-dmpea
Steady interest

#1,340 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Dextromethorphan HBr, Guaifenesin
Top half

#718 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 N,n-dmpea

What is N,n-dmpea?

  • Mood or energy support
  • Pre-workout or stimulant effect
  • Cognitive or focus support

N,N-DMPEA (N,N-dimethylphenethylamine) is a synthetic relative of phenethylamine sometimes marketed in stimulant or pre-workout supplements. There is very little reliable human research on its effects or safety, and it is not a well-established dietary ingredient, so it should be approached with real caution.

Read the full N,n-dmpea monograph & all interactions
Keep checking

Other Drugs & N,n-dmpea

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

0Major
192Moderate
0Minor
2,637No known interaction
192 Moderate 2,637 No interaction
Moderate

192 interactions

Showing 60 of 192 moderate interactions — see all 192 on the N,n-dmpea page.

No interaction 2,637 drugs checked — show the list

We also checked N,n-dmpea against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,637 medications checked with no known interaction — see the full N,n-dmpea list.

See the full N,n-dmpea 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
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Pharmacist Counseling Corner

Taking N,n-dmpea and Dextromethorphan HBr, Guaifenesin Together: Common Questions

Can you take N,n-dmpea 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.
How serious is the N,n-dmpea 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

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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.