Drug & supplement interaction

Knotweed + Macitentan

Macitentan brand name: Opsumit.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Oct 4, 2026
The bottom line No known interaction

We found no known interaction between Knotweed and Macitentan in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Knotweed and Macitentan

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Macitentan and Knotweed in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

Worth understanding: our licensed dataset holds no drug-interaction record for Knotweed at all — not against Macitentan, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Knotweed safety at a glance

Knotweed overall Use caution May be reasonably tolerated short-term, but human safety data are limited and it can cause digestive side effects.
Pregnancy Avoid Not enough safety information; some compounds may affect the uterus, so avoid during pregnancy.
Breastfeeding Avoid There is not enough safety information, so avoid use while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Macitentan and Knotweed? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Macitentan’s Own FDA Label Lists

This is not an interaction — none of it involves Knotweed. These are the most notable effects listed in the ADVERSE REACTIONS section of Macitentan’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both. 6 of them are worth acting on rather than waiting out — marked below.

  • Heart failure Worth acting on
  • Anemia Worth acting on
  • A severe allergic reaction Worth acting on
  • A higher chance of infection Worth acting on mentioned in 6.6% of FDA reports for Macitentan
  • Liver problems Worth acting on
  • An allergic reaction Worth acting on
  • Flushing
  • A stuffy or runny nose
  • Sore throat
  • Low blood pressure

Showing the 10 most notable of 14 label-listed effects — ranked by how unusual each one is across medicines generally, with serious effects weighted up.

From the ADVERSE REACTIONS section of the FDA label for Macitentan. Read the label on DailyMed › Where a percentage is shown, it is the share of 68,860 voluntary FDA FAERS reports for Macitentan that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Knotweed’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Knotweed side to compare — that is a limit of the record, not a statement that Knotweed has no side effects.

Everything else you take

See Every Supplement That Interacts With Macitentan

This page covers Knotweed 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 Knotweed as Part of a Dietary Supplement Product? Check It for Interactions

We hold 46 real supplement products containing Knotweed, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Knotweed. Even though Knotweed itself has no known interaction with Macitentan, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Knotweed 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 Knotweed
Steady interest

#1,026 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Macitentan
Top 25%

#598 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Knotweed reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified October 4, 2026. The Knotweed and Macitentan records this page draws on were last updated June 22, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Knotweed

What is Knotweed?

  • Source of resveratrol
  • Heart and circulation support
  • Lyme disease support (traditional/herbalist use)
  • Inflammation
  • Traditional Chinese medicine remedies

Japanese knotweed (Polygonum cuspidatum) is an herb best known as a natural source of resveratrol and emodin, and it is used in traditional Chinese medicine and by some herbalists. Human evidence for most modern health claims is limited, and it can cause digestive upset, so talk with your pharmacist or doctor before using it.

Polygonum cuspidatum · Polygonaceae · Roots and rhizomes (most common); also leaves and stems · Capsules, tablets, powdered root extract, tinctures, teas

An interaction check asks whether these two react with each other — it does not ask whether Knotweed is a good idea for someone in your situation. Here is what our Knotweed record says about it on its own.

Knotweed: dosing

There is no official, well-established dose for knotweed. The right amount depends on the product, how it is prepared, and how much resveratrol or other active compound it contains.Because extracts vary widely in strength, the safest approach is to follow the directions on the product label and not exceed them. A pharmacist or doctor can help you decide whether knotweed is appropriate for you and what amount may be reasonable. Choose products from reputable companies that test for quality and clearly list the species used.

From our Knotweed monograph — the full record covers uses, side effects and every documented interaction.

Read the full Knotweed 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 type of high blood pressure in the arteries of the lungs. The goal is to slow the disease from getting worse and to lower the chance of being hospitalized because of PAH.

In the key clinical study, macitentan was used in adults with mainly moderate-to-severe PAH symptoms. Patients had PAH caused by unknown or inherited causes, connective tissue disorders, or congenital heart disease with repaired shunts.

Most-Reported Side Effects for Macitentan

From FAERS, the FDA’s public side-effect reporting system (68,860 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Dyspnea 11,958 reports
Headache 8,323 reports
Diarrhea 6,584 reports
Nausea 5,972 reports
Fatigue 5,041 reports
See full Macitentan drug information
Keep checking

Other Drugs & Knotweed

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Knotweed list.

See the full Knotweed interactions page
See every supplement checked against Macitentan, ranked by severity
Evidence & sources

Knotweed References

The 1 references that drive our Knotweed monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Gonzalez Begne M, Yslas N, Reyes E, et al. Clinical effect of a Mexican sanguinaria (Polygonum aviculare L.) on gingivitis. J Ethnopharmacol 2001;74:45-51..

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Knotweed and Macitentan Together: Common Questions

Is it safe to take Knotweed with Macitentan?
We do not list a known interaction between Knotweed and Macitentan. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Does Macitentan interact with any supplements?
Yes. Macitentan has documented interactions with 253 supplements in our database — Knotweed is not one of them. The Macitentan interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Knotweed monograph Uses, safety profile, and every drug interaction in one place Macitentan drug information The full plain-English guide to this medication Macitentan supplement interactions Every supplement checked against Macitentan, 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 References The 1 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Macitentan and Knotweed?

Our pharmacists answer your medication & supplement questions — free.

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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.