Drug & supplement interaction

False Unicorn + Dextromethorphan HBr, Phenylephrine HCl

Dextromethorphan HBr, Phenylephrine HCl brand name: Vicks Formula 44D Cough & Head Congestion Relief.

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

Dextromethorphan HBr, Phenylephrine HCl falls into 2 drug categories that False Unicorn can interact with; the most serious is rated moderate. In vitro, false unicorn extract inhibits cytochrome P450 2D6 (CYP2D6) activity.

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

False Unicorn and Dextromethorphan HBr, Phenylephrine HCl

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

Why Are There 2 Interactions?

False Unicorn interacts with whole categories of medication. Dextromethorphan HBr, Phenylephrine HCl falls into 2 of those categories, so it can interact with False Unicorn 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, Phenylephrine HCl

Dextromethorphan HBr, Phenylephrine HCl falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES — the group False Unicorn interacts with.

In vitro, false unicorn extract inhibits cytochrome P450 2D6 (CYP2D6) activity. Theoretically, false unicorn might increase the levels of CYP2D6 substrates. Some of drugs that are CYP2D6 substrates 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 for your cough syrup. The dextromethorphan part of Formula 44D is cleared from your body mainly by a liver enzyme called CYP2D6. In lab (test tube) studies, False Unicorn appears to slow that enzyme down. If that held true in people, dextromethorphan could build up and linger longer than usual, which might mean more dizziness, drowsiness, or feeling foggy and lightheaded.

I want to be honest about how soft this evidence is. So far it's only test tube data, not real-world cases, so the actual risk for most folks is probably low. The phenylephrine (decongestant) piece isn't really affected here. Still, since safety of False Unicorn isn't well studied, run this combo by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Ho SH, Singh M, Holloway AC, Crankshaw DJ. The effects of commercial preparations of herbal supplements commonly used by women on the biotransformation of fluorogenic substrates by human cytochromes P450. Phytother Res. 2011;25(7):983-9. PubMed
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

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

In vitro, false unicorn extract inhibits cytochrome P450 3A4 (CYP3A4) activity. Theoretically, false unicorn might increase the levels of CYP3A4 substrates. Drugs that might be affected include some calcium channel blockers (diltiazem, nicardipine, verapamil), chemotherapeutic agents (etoposide, paclitaxel, vinblastine, vincristine, vindesine), antifungals (ketoconazole, itraconazole), glucocorticoids, cisapride (Propulsid), alfentanil (Alfenta), fentanyl (Sublimaze), losartan (Cozaar), fluoxetine (Prozac), midazolam (Versed), omeprazole (Prilosec), ondansetron (Zofran), propranolol (Inderal), fexofenadine (Allegra), 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 Vicks Formula 44D, which pairs dextromethorphan (the cough suppressant) with phenylephrine (the decongestant). The concern is that False Unicorn, at least in a test tube, can slow down a liver enzyme called CYP3A4 that helps clear dextromethorphan. If that enzyme is blocked, a little more dextromethorphan could linger in your system, which might mean more drowsiness, dizziness, or feeling foggy.

I want to be honest about how thin this evidence is. It comes only from lab studies, not from real people, so we don't actually know if it matters in practice. Neither drug here is a prodrug, so the direction is straightforward (slightly higher levels, not lower). Still, with the cold-and-flu season being short-term use, it's worth a quick chat with your pharmacist before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Ho SH, Singh M, Holloway AC, Crankshaw DJ. The effects of commercial preparations of herbal supplements commonly used by women on the biotransformation of fluorogenic substrates by human cytochromes P450. Phytother Res. 2011;25(7):983-9. 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

False Unicorn Also Interacts With Other Medications

False Unicorn has 739 moderate known drug interactions in our database — the Dextromethorphan HBr, Phenylephrine HCl one above is among them. If you take anything else, check it against the full list below.

Moderate 739 No known interaction 2,091 (incl. Dextromethorphan HBr, Phenylephrine HCl)
Taking anything else?

Check Another of Your Medications Against False Unicorn

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

Everything else you take

See Every Supplement That Interacts With Dextromethorphan HBr, Phenylephrine HCl

This page covers False Unicorn only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dextromethorphan HBr, Phenylephrine HCl 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 HBr, Phenylephrine HCl page

“The supplement interactions with Dextromethorphan HBr and Phenylephrine HCl (Vicks Formula 44D) deserve real respect, and the small cluster of major-rated ones should be understood before you reach for the bottle. Phenylephrine is a stimulant-type decongestant, so anything with caffeine (coffee, tea, cola nut) or ephedrine-like herbs s…”

Reviewed by 2 · Jul 18, 2026

Open the Dextromethorphan HBr, Phenylephrine HCl interaction page

One more smart check

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

We hold 32 real supplement products containing False Unicorn, each one broken down to its full ingredient list — and combination products often carry several ingredients besides False Unicorn. Your product may carry other ingredients that interact with Dextromethorphan HBr, Phenylephrine HCl too, on top of False Unicorn — 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 False Unicorn and Dextromethorphan HBr, Phenylephrine HCl 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 False Unicorn
Top half

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

29 days ago today
Medication Dextromethorphan HBr, Phenylephrine HCl
Steady interest

#2,704 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 False Unicorn

What is False Unicorn?

False Unicorn
  • Menstrual cramps
  • Menopausal symptoms
  • Female infertility support
  • Irregular periods
  • Digestive complaints

False Unicorn is a North American plant whose root has long been used in traditional medicine for women's reproductive and menstrual concerns. There is very little reliable human research to show it actually works, and safety has not been well studied, so it should be used with caution and never during pregnancy. Talk to your pharmacist or doctor before trying it.

Read the full False Unicorn monograph & all interactions
Keep checking

Other Drugs & False Unicorn

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

0Major
739Moderate
0Minor
2,090No known interaction
739 Moderate 2,090 No interaction
Moderate

739 interactions

Showing 60 of 739 moderate interactions — see all 739 on the False Unicorn page.

No interaction 2,090 drugs checked — show the list

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

Showing the 60 most looked-up of 2,090 medications checked with no known interaction — see the full False Unicorn list.

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

Can you take False Unicorn with Dextromethorphan HBr, Phenylephrine HCl?
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 False Unicorn and Dextromethorphan HBr, Phenylephrine HCl?
Dextromethorphan HBr, Phenylephrine HCl belongs to more than one drug category, and False Unicorn 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 False Unicorn and Dextromethorphan HBr, Phenylephrine HCl 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.