Drug & supplement interaction

Eucalyptus + Dextromethorphan

Dextromethorphan brand names: Hold, Benylin Adult, Benylin Pediatric, Theraflu Thin Strips Long Acting Cough, Neo Citran Thin Strips Cough.

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

Eucalyptus has a moderate interaction with Dextromethorphan. Theoretically, eucalyptus might increase the levels of CYP3A4 substrates.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Eucalyptus and Dextromethorphan

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

Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

Why this applies to Dextromethorphan

Dextromethorphan falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES — the group Eucalyptus interacts with.

Theoretically, eucalyptus might increase the levels of CYP3A4 substrates.
In vitro research suggests that eucalyptus oil might inhibit CYP3A4, although 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: your body clears dextromethorphan partly through a liver enzyme called CYP3A4. Lab-dish studies hint that eucalyptus oil might slow that enzyme down. If that happened in real life, dextromethorphan could linger a bit longer and build up, which might mean stronger or longer side effects like drowsiness, dizziness, mild stomach upset, or feeling foggy.

I want to be honest about the strength of this, though. This is only a theoretical concern from test-tube research, and it has never actually been seen in people. Sniffing eucalyptus in a vapor rub or lozenge is very unlikely to cause a problem. Still, if you're using concentrated eucalyptus oil supplements, 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. Unger M, Frank A. Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction. Rapid Commun Mass Spectrom 2004;1 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

Eucalyptus Also Interacts With Other Medications

Eucalyptus has 877 moderate known drug interactions in our database — the Dextromethorphan one above is one of them. If you take anything else, check it against the full list below.

Moderate 877 No known interaction 1,953 (incl. Dextromethorphan)
Taking anything else?

Check Another of Your Medications Against Eucalyptus

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

From our Q&A

Questions About Eucalyptus or Dextromethorphan

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Eucalyptus or Dextromethorphan, 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

This page covers Eucalyptus only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dextromethorphan 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 page

“A glass of grapefruit juice can push dextromethorphan (Benylin, Hold, and other cough medicines) to higher levels than intended, one of four major-rated entries among the 171 supplements and herbs on file, and the list as a whole warrants real care. Most interactions trace back to the liver enzymes (CYP3A4 and CYP2D6) that clear dextro…”

Reviewed by 2 · Jul 18, 2026

Open the Dextromethorphan interaction page

One more smart check

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

We hold 216 real supplement products containing Eucalyptus, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Eucalyptus. Your product may carry other ingredients that interact with Dextromethorphan too, on top of Eucalyptus — 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 Eucalyptus and Dextromethorphan 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 Eucalyptus
Top 25%

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

29 days ago today
Medication Dextromethorphan
Top 5%

#80 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 Eucalyptus

What is Eucalyptus?

Eucalyptus
  • Cough and chest congestion
  • Colds and flu symptoms
  • Stuffy nose
  • Sore throat
  • Minor muscle and joint aches
  • Aromatherapy

Eucalyptus is best known for its strong-smelling oil used in vapor rubs, inhalants, and lozenges to ease coughs and congestion. It may provide mild, short-term relief of cold symptoms, but the oil is toxic if swallowed and must never be taken by mouth undiluted. Talk to a pharmacist or doctor before using it, especially in children, during pregnancy, or while breastfeeding.

Read the full Eucalyptus monograph & all interactions
Medication

About Dextromethorphan

What Is Dextromethorphan Used For?

Brand names: Hold, Benylin Adult, Benylin Pediatric, Theraflu Thin Strips Long Acting Cough, Neo Citran Thin Strips Cough

Dextromethorphan temporarily relieves cough due to minor throat and bronchial irritation, such as the kind that comes with the common cold or breathing in irritants. It also helps reduce the urge to cough so you — or your child — can get to sleep.

Some products, including CVS Long Acting Cough and Premier Value Tussin Cough oral liquids, are also indicated to help loosen phlegm (mucus) and thin bronchial secretions to help drain the airways.

See full Dextromethorphan drug information
Keep checking

Other Drugs & Eucalyptus

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

0Major
877Moderate
0Minor
1,952No known interaction
877 Moderate 1,952 No interaction
Moderate

877 interactions

Showing 60 of 877 moderate interactions — see all 877 on the Eucalyptus page.

No interaction 1,952 drugs checked — show the list

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

Showing the 60 most looked-up of 1,952 medications checked with no known interaction — see the full Eucalyptus list.

See the full Eucalyptus interactions page
See every supplement checked against Dextromethorphan, 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
Eucalyptus monograph › Uses, safety, and every drug interaction in one place Dextromethorphan supplement interactions › Every supplement checked against Dextromethorphan, ranked by severity Dextromethorphan drug information › The full plain-English guide to this medication 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 Eucalyptus and Dextromethorphan Together: Common Questions

Can you take Eucalyptus with Dextromethorphan?
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 Eucalyptus and Dextromethorphan 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 and Eucalyptus?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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.