Drug & supplement interaction

Horny Goat Weed + Macitentan

Macitentan brand name: Opsumit.

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

Macitentan falls into 2 drug categories that Horny Goat Weed can interact with; the most serious is rated moderate. Theoretically, horny goat weed might increase the risk of hypotension.

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

Horny Goat Weed and Macitentan

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

Why Are There 2 Interactions?

Horny Goat Weed interacts with whole categories of medication. Macitentan falls into 2 of those categories, so it can interact with Horny Goat Weed in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

ANTIHYPERTENSIVE DRUGS

1 of 2

Why this applies to Macitentan

Macitentan falls under ANTIHYPERTENSIVE DRUGS — the group Horny Goat Weed interacts with.

Theoretically, horny goat weed might increase the risk of hypotension.
Laboratory research suggests that horny goat weed might have hypotensive effects. This effect 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

Macitentan (Opsumit) is already designed to relax and widen your blood vessels to ease the pressure in your lungs, which naturally lowers blood pressure as part of how it works. Here's the concern: in lab studies, horny goat weed seemed to have its own blood-pressure-lowering effect too. Stack the two together and, in theory, your pressure could dip a little more than expected.

I want to be honest about the evidence here, though. This blood-pressure effect from horny goat weed has only shown up in test-tube and animal research, not in actual people. So this is more of a theoretical caution than something we see happening regularly. Still, if you ever feel dizzy, lightheaded, or faint, that's worth paying attention to. Please check with your pharmacist or doctor before adding this supplement.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Cirigliano MD, Szapary PO. Horny goat weed for erectile dysfunction. Alt Med Alert 2001;4:19-22.
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

Macitentan also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, horny goat weed might increase the effects and side effects of CYP3A4 substrates.
In vitro, horny goat weed extract inhibits CYP3A4 and suppresses CYP3A4 mRNA expression. This effect 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 for Macitentan (Opsumit). Your body uses an enzyme called CYP3A4 to break this medicine down. In test-tube studies, horny goat weed appears to slow that same enzyme. If that happened in real life, your macitentan could clear more slowly and build up, which might make its effects and side effects stronger, things like low blood pressure, headache, swelling in the legs, a stuffy nose, or low red blood cell counts (anemia).

The honest part: this is only lab evidence, and it has not been shown in people, so I wouldn't lose sleep over it. Still, because PAH is serious and macitentan matters, it's worth a quick chat with your pharmacist or doctor before adding this herb.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Li K, Yu XH, Maskey AR, et al. Cytochrome P450 3A4 suppression by epimedium and active compound kaempferol leads to synergistic anti-inflammatory effect with corticosteroid. Front Pharmacol 2023;13:1042756. 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

Horny Goat Weed Also Interacts With Other Medications

Horny Goat Weed has 962 moderate known drug interactions in our database — the Macitentan one above is among them. If you take anything else, check it against the full list below.

Moderate 962 No known interaction 1,868 (incl. Macitentan)
Taking anything else?

Check Another of Your Medications Against Horny Goat Weed

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

From our Q&A

Questions About Horny Goat Weed or Macitentan

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

This page covers Horny Goat Weed only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Macitentan page lists 253 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), Beer (major) and Grapefruit (major).

By severity: 9 major · 205 moderate · 39 minor.

From our pharmacist’s overview on the Macitentan page

“If you take macitentan (Opsumit) for pulmonary arterial hypertension, study this page rather than skim it. It lists 253 supplement and herbal ingredients, nine rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Macitentan interaction page

One more smart check

Taking Horny Goat Weed as Part of a Dietary Supplement Product? Check It for Interactions

We hold 183 real supplement products containing Horny Goat Weed, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Horny Goat Weed. Your product may carry other ingredients that interact with Macitentan too, on top of Horny Goat Weed — 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 Horny Goat Weed and Macitentan 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 Horny Goat Weed
Top 25%

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

29 days ago today
Medication Macitentan
Top 5%

#103 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 Horny Goat Weed

What is Horny Goat Weed?

Horny Goat Weed
  • Erectile dysfunction
  • Low libido
  • Fatigue and low energy
  • Bone health
  • Joint and menopausal symptoms
  • General 'vitality' or performance

Horny goat weed (Epimedium) is a traditional Chinese herb most often marketed for low libido and erectile problems, but solid human evidence for these uses is lacking. While short-term use seems generally tolerated by some people, quality and safety are not well studied, so talk to your pharmacist or doctor before trying it—especially if you have heart problems or take other medicines.

Read the full Horny Goat Weed monograph & all interactions
Medication

About Macitentan

What Is Macitentan Used For?

Brand name: Opsumit

Macitentan tablets — sold under the brand name Opsumit — are used to treat pulmonary arterial hypertension (PAH, WHO Group I), a serious condition where the blood pressure in the arteries supplying the lungs is abnormally high. The goal is to slow down how quickly the disease gets worse and to lower the chances of being hospitalized because of it.

In clinical studies, it was shown to be effective in adults with mostly moderate-to-severe PAH symptoms. Patients in those studies had PAH caused by unknown or inherited reasons, connective tissue disorders, or congenital heart disease with repaired heart shunts.

See full Macitentan drug information
Keep checking

Other Drugs & Horny Goat Weed

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

0Major
962Moderate
0Minor
1,867No known interaction
962 Moderate 1,867 No interaction
Moderate

962 interactions

Showing 60 of 962 moderate interactions — see all 962 on the Horny Goat Weed page.

No interaction 1,867 drugs checked — show the list

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

Showing the 60 most looked-up of 1,867 medications checked with no known interaction — see the full Horny Goat Weed list.

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

Can you take Horny Goat Weed with Macitentan?
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 Horny Goat Weed and Macitentan?
Macitentan belongs to more than one drug category, and Horny Goat Weed 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 Horny Goat Weed and Macitentan 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 Macitentan and Horny Goat Weed?

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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.