Drug & supplement interaction

Black Pepper + Dextromethorphan, Guaifenesin, Psuedoephedrine

Dextromethorphan, Guaifenesin, Psuedoephedrine brand name: Aquatab C.

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

Dextromethorphan, Guaifenesin, Psuedoephedrine falls into 2 drug categories that Black Pepper can interact with; the most serious is rated moderate. Theoretically, black pepper might increase levels of drugs metabolized by CYP2D6.

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

Black Pepper and Dextromethorphan, Guaifenesin, Psuedoephedrine

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

Why Are There 2 Interactions?

Black Pepper interacts with whole categories of medication. Dextromethorphan, Guaifenesin, Psuedoephedrine falls into 2 of those categories, so it can interact with Black Pepper 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, Guaifenesin, Psuedoephedrine

Dextromethorphan, Guaifenesin, Psuedoephedrine falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES — the group Black Pepper interacts with.

Theoretically, black pepper might increase levels of drugs metabolized by CYP2D6.
In vitro research suggests that some constituents of black pepper inhibit CYP2D6. This has not been reported in humans.
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

Of the three ingredients in Aquatab C, the one to focus on here is dextromethorphan (the cough suppressant). Your body relies on a liver enzyme called CYP2D6 to clear it. Lab studies hint that piperine, the active part of black pepper, might slow that enzyme down. If that happened, more dextromethorphan could linger in your system, which could mean extra drowsiness, dizziness, or a foggy, lightheaded feeling. Guaifenesin and pseudoephedrine aren't really affected by this.

The good news: this is only a theory drawn from test-tube work, and it hasn't actually shown up in people. Everyday pepper on your food shouldn't matter. If you take concentrated piperine or curcumin supplements, just mention it to your pharmacist to be safe.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Subehan, Usia, T., Kadota, S., and Tezuka, Y. Mechanism-based inhibition of human liver microsomal cytochrome P450 2D6 (CYP2D6) by alkamides of Piper nigrum. Planta Med 2006;72(6):527-532.
  2. Usia, T., Iwata, H., Hiratsuka, A., Watabe, T., Kadota, S., and Tezuka, Y. CYP3A4 and CYP2D6 inhibitory activities of Indonesian medicinal plants. Phytomedicine. 2006;13(1-2):67-73. PubMed
  3. Subehan, Usia, T., Iwata, H., Kadota, S., and Tezuka, Y. Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants. J Ethnopharmacol. 5-24-2006;105(3):449-455. PubMed
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

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

Theoretically, black pepper might increase levels of drugs metabolized by CYP3A4.
In vitro research and pharmacokinetic simulation data suggest that piperine, a constituent of black pepper, as well as the pepper fruit seem to inhibit CYP3A4. This has not been reported in humans.
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 simple version: piperine, the compound that gives black pepper its kick, may slow down a liver enzyme called CYP3A4 in lab studies. One ingredient in your Aquatab C, dextromethorphan, partly relies on that pathway. So in theory, concentrated black pepper supplements could let a bit more dextromethorphan linger in your body, which might mean more drowsiness, dizziness, or feeling foggy.

I want to be honest, though: this is based only on test-tube and computer-model data, not real people. Sprinkling pepper on your food is not a concern. The guaifenesin and pseudoephedrine parts aren't really affected. If you take a strong piperine supplement (often paired with turmeric), just run it by your pharmacist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Bhardwaj RK, Glaeser H, Becquemont L, et al. Piperine, a major constituent of black pepper, inhibits human P-glycoprotein and CYP3A4. J Pharmacol Exp Ther 2002;302:645-50. PubMed
  2. Usia, T., Iwata, H., Hiratsuka, A., Watabe, T., Kadota, S., and Tezuka, Y. CYP3A4 and CYP2D6 inhibitory activities of Indonesian medicinal plants. Phytomedicine. 2006;13(1-2):67-73. PubMed
  3. Lin F, Hu Y, Zhang Y, Zhao L, Zhong D, Liu J. Predicting Food-Drug Interactions between Piperine and CYP3A4 Substrate Drugs Using PBPK Modeling. Int J Mol Sci 2024;25(20):10955. 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

Black Pepper Also Interacts With Other Medications

Black Pepper has 975 moderate, 43 minor known drug interactions in our database — the Dextromethorphan, Guaifenesin, Psuedoephedrine one above is among them. If you take anything else, check it against the full list below.

Moderate 975 Minor 43 No known interaction 1,812 (incl. Dextromethorphan, Guaifenesin, Psuedoephedrine)
Taking anything else?

Check Another of Your Medications Against Black Pepper

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

From our Q&A

Questions About Black Pepper or Dextromethorphan, Guaifenesin, Psuedoephedrine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Black Pepper or Dextromethorphan, Guaifenesin, Psuedoephedrine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Dextromethorphan, Guaifenesin, Psuedoephedrine

This page covers Black Pepper only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dextromethorphan, Guaifenesin, Psuedoephedrine page lists 197 supplements it has a documented interaction with, worst first, each one explained.

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

By severity: 8 major · 148 moderate · 41 minor.

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

“A cold and congestion remedy sounds low stakes, but Aquatab C (dextromethorphan, guaifenesin, and pseudoephedrine) earns real caution. Eight of the 197 supplements and herbs on file carry a major rating, and those deserve your attention first.”

Reviewed by 2 · Jul 18, 2026

Open the Dextromethorphan, Guaifenesin, Psuedoephedrine interaction page

One more smart check

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

We hold 5,528 real supplement products containing Black Pepper, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Black Pepper. Your product may carry other ingredients that interact with Dextromethorphan, Guaifenesin, Psuedoephedrine too, on top of Black Pepper — 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 Black Pepper and Dextromethorphan, Guaifenesin, Psuedoephedrine 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 Black Pepper
Top 5%

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

29 days ago today
Medication Dextromethorphan, Guaifenesin, Psuedoephedrine
Top 10%

#148 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 Black Pepper

What is Black Pepper?

Black Pepper
  • Flavoring and culinary use
  • Digestive complaints like bloating and indigestion
  • Boosting absorption of other supplements
  • Antioxidant and anti-inflammatory support
  • Cold and congestion remedies

Black pepper is a common kitchen spice that is generally safe in the amounts used in food. Its extract, piperine, is mostly added to supplements to help the body absorb other ingredients (like curcumin from turmeric). Strong human evidence for black pepper treating specific health conditions is limited, so use supplement-strength products with care and check with your pharmacist.

Read the full Black Pepper monograph & all interactions
Keep checking

Other Drugs & Black Pepper

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

0Major
975Moderate
43Minor
1,811No known interaction
975 Moderate 43 Minor 1,811 No interaction
Moderate

975 interactions

Showing 60 of 975 moderate interactions — see all 975 on the Black Pepper page.

Minor

43 interactions

No interaction 1,811 drugs checked — show the list

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

Showing the 60 most looked-up of 1,811 medications checked with no known interaction — see the full Black Pepper list.

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

Can you take Black Pepper with Dextromethorphan, Guaifenesin, Psuedoephedrine?
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 Black Pepper and Dextromethorphan, Guaifenesin, Psuedoephedrine?
Dextromethorphan, Guaifenesin, Psuedoephedrine belongs to more than one drug category, and Black Pepper 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 Black Pepper and Dextromethorphan, Guaifenesin, Psuedoephedrine 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, Guaifenesin, Psuedoephedrine and Black Pepper?

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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.