Drug & supplement interaction

White Horehound + Epoprostenol

Epoprostenol brand name: Flolan.

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

White Horehound has a moderate interaction with Epoprostenol. Evidence from animal research suggests that taking white horehound extract lowers blood pressure.

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

White Horehound and Epoprostenol

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

Moderate

ANTIHYPERTENSIVE DRUGS

Why this applies to Epoprostenol

Epoprostenol falls under ANTIHYPERTENSIVE DRUGS — the group White Horehound interacts with.

Evidence from animal research suggests that taking white horehound extract lowers blood pressure. Theoretically, taking white horehound with antihypertensive drugs might enhance therapeutic effects and increase the risk of hypotension. Some antihypertensive drugs include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), Amlodipine (Norvasc), hydrochlorothiazide (HydroDiuril), furosemide (Lasix), and many 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 thing to keep in mind. Epoprostenol (Flolan) is a powerful medicine given through a continuous IV pump to widen blood vessels and lower pressure in the lungs for pulmonary hypertension. On its own it can already lower your blood pressure and cause flushing, headache, dizziness, jaw pain, and nausea.

White horehound has been shown in animal studies only to nudge blood pressure down a bit, so the worry is mostly theoretical. Still, stacking it on top of Epoprostenol could in theory add to the blood-pressure-lowering effect and leave you feeling lightheaded or faint. Because this drug is so carefully dose-adjusted, I'd run any horehound product, even cough drops, past your doctor or pharmacist first rather than starting it on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. El Bardai, S., Lyoussi, B., Wibo, M., and Morel, N. Pharmacological evidence of hypotensive activity of Marrubium vulgare and Foeniculum vulgare in spontaneously hypertensive rat. Clin Exp Hypertens. 2001;23(4):329-343.
  2. El Bardai, S., Lyoussi, B., Wibo, M., and Morel, N. Comparative study of the antihypertensive activity of Marrubium vulgare and of the dihydropyridine calcium antagonist amlodipine in spontaneously hypertensive rat. Clin Exp Hypertens. 2004;26(6):465-474 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

White Horehound Also Interacts With Other Medications

White Horehound has 257 moderate known drug interactions in our database — the Epoprostenol one above is one of them. If you take anything else, check it against the full list below.

Moderate 257 No known interaction 2,573 (incl. Epoprostenol)
Taking anything else?

Check Another of Your Medications Against White Horehound

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

Everything else you take

See Every Supplement That Interacts With Epoprostenol

This page covers White Horehound only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Epoprostenol page lists 136 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Tyramine (major) and Adrafinil (moderate).

By severity: 4 major · 111 moderate · 21 minor.

From our pharmacist’s overview on the Epoprostenol page

“American hellebore tops my concerns for anyone on epoprostenol (Flolan), the continuous infusion that opens blood vessels in the lungs to treat pulmonary arterial hypertension. The herb lowers blood pressure even in small doses, and stacked on a medicine that already relaxes those vessels, the drop can be dangerous.”

Reviewed by 2 · Jul 18, 2026

Open the Epoprostenol interaction page

How much people look this up

Where White Horehound and Epoprostenol 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 White Horehound
Steady interest

#1,037 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Epoprostenol
Top 25%

#678 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 White Horehound

What is White Horehound?

White Horehound
  • Cough and chest congestion
  • Sore throat
  • Bronchitis
  • Digestive upset and poor appetite
  • Bloating and gas

White horehound is a traditional bitter herb used mainly for coughs, sore throats, and mild digestive complaints, and it is a common flavoring in old-fashioned cough drops. Solid human evidence supporting these uses is limited, so view it as a folk remedy rather than a proven treatment. Talk to your pharmacist or doctor before using it, and avoid it during pregnancy.

Read the full White Horehound monograph & all interactions
Medication

About Epoprostenol

What Is Epoprostenol Used For?

Brand name: Flolan

Epoprostenol (available as the brands Epoprostenol, Flolan, and Veletri) is used to treat pulmonary arterial hypertension (PAH) — WHO Group 1, a type of high blood pressure in the arteries of the lungs. The goal is to improve how much physical activity patients can handle.

The clinical studies that established its effectiveness included mainly patients with moderate-to-severe symptoms (NYHA Functional Class III–IV) whose PAH was idiopathic (no known cause), heritable (genetic), or related to connective tissue diseases such as scleroderma.

See full Epoprostenol drug information
Keep checking

Other Drugs & White Horehound

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

0Major
257Moderate
0Minor
2,572No known interaction
257 Moderate 2,572 No interaction
Moderate

257 interactions

Showing 60 of 257 moderate interactions — see all 257 on the White Horehound page.

No interaction 2,572 drugs checked — show the list

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

Showing the 60 most looked-up of 2,572 medications checked with no known interaction — see the full White Horehound list.

See the full White Horehound interactions page
See every supplement checked against Epoprostenol, 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
White Horehound monograph › Uses, safety, and every drug interaction in one place Epoprostenol supplement interactions › Every supplement checked against Epoprostenol, ranked by severity Epoprostenol 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 White Horehound and Epoprostenol Together: Common Questions

Can you take White Horehound with Epoprostenol?
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 White Horehound and Epoprostenol 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 Epoprostenol and White Horehound?

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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.