Belumosudil and St John's Wort: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 15, 2026 · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
St John's Wort
No brand names on recordBelumosudil
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
St. John's Wort can make belumosudil (Rezurock) work less well. St. John's Wort, an herbal supplement, speeds up a liver enzyme (called CYP3A) that breaks down belumosudil. When that enzyme works faster, more of your belumosudil gets cleared out before it can do its job. In a study, this dropped drug levels by roughly 60 to 70 percent.
Belumosudil is used to treat chronic graft-versus-host disease, so keeping it working is important. The good news is your care team can manage this. Please don't stop or change anything on your own, but do tell your pharmacist or doctor about any herbal supplements you take so they can adjust your plan.
Effect: St. John's Wort (strong CYP3A inducer) increases CYP3A-mediated metabolism of belumosudil (CYP3A substrate), reducing belumosudil exposure and potentially its efficacy.
- Direction: Enzyme induction, decreased exposure (reduced effect). Neither is a prodrug.
- Magnitude: With rifampin, belumosudil Cmax decreased 59% and AUC 72%.
- Evidence: Probable; severity major; onset unspecified (induction typically develops over days to weeks).
- Management: If coadministered with a strong CYP3A inducer, increase belumosudil to 200 mg twice daily. Monitor for reduced clinical response (cGVHD control).
What happens
Reduced belumosudil exposure and reduced efficacy of belumosudil
Interaction Deep Dive
Taking belumosudil (a CYP3A substrate) together with a strong CYP3A inducer can lower belumosudil exposure, potentially diminishing its efficacy. A drug interaction study conducted in healthy subjects showed that when belumosudil was given alongside rifAMPin (a strong CYP3A inducer), belumosudil Cmax fell by 59% and AUC dropped by 72%. When belumosudil is used concurrently with a strong CYP3A inducer, raise the belumosudil dose to 200 mg twice daily1.
Why it happens (mechanism)
Induction of CYP3A-mediated belumosudil metabolism
How to manage this interaction
What your care team may do:
- Because St. John's Wort can lower belumosudil levels, the label recommends increasing belumosudil to 200 mg twice daily when taken with a strong CYP3A inducer. Your team will individualize this.
- They may watch your response more closely to make sure your treatment is still working.
- An alternative may be avoiding St. John's Wort altogether, which your prescriber can advise on.
What you should do: Keep taking belumosudil exactly as prescribed, and tell your pharmacist or doctor before starting or stopping St. John's Wort or any supplement. Do not change your dose on your own.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a drug interaction study conducted in healthy subjects, coadministration of belumosudil with rifAMPin (a strong CYP3A inducer) reduced belumosudil Cmax by 59% and AUC by 72% 1.
Common questions
Can I take Belumosudil and St John's Wort together?
St. John's Wort can significantly lower belumosudil levels and may reduce its effectiveness; tell your care team, since the dose can be increased to 200 mg twice daily and your response monitored. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Belumosudil and St John's Wort interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Belumosudil and St John's Wort interaction managed?
What your care team may do: Because St. John's Wort can lower belumosudil levels, the label recommends increasing belumosudil to 200 mg twice daily when taken with a strong CYP3A inducer. Your team will individualize this. They may watch your response more closely to make sure your treatment is still working. An alternative may be avoiding St. John's Wort altogether, which your prescriber can advi… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Belumosudil or St John's Wort need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: REZUROCK(R) oral tablets, belumosudil oral tablets. Kadmon Pharmaceuticals LLC (per FDA), Bridgewater, NJ, 2024. DailyMed
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