The short answer
St. John's wort can lower oral verapamil exposure and may reduce its effectiveness. The cited guidance advises checking with a pharmacist or prescriber before taking it; the small human study did not measure how often treatment fails.
What this answer covers
Applies to oral verapamil; the study used repeated St. John's wort dosing for 14 days, and effects can vary with the botanical preparation.
- Supplement or preparation
- St. John's wort
- Medication ingredient
- verapamil
Evidence and practical considerations
Absorption & effectiveness
An exact controlled human PK study and current guidance support reduced oral verapamil exposure and possible reduced effectiveness.
- Exact scope
- St. John's wort with verapamil
- Medication form and route
- oral
- Timing or duration
- The controlled study used St. John's wort 300 mg three times daily for 14 days before verapamil assessment.
What remains uncertain
- The interaction affects first-pass metabolism rather than the fraction absorbed through the intestinal wall.
- Magnitude may vary by St. John's wort preparation and hyperforin content.
Factors that may matter: high-hyperforin St. John's wort product; longer co-use; narrow therapeutic response target; unstable blood pressure or arrhythmia control.
Read the supporting source summaries
Source 1: controlled human pharmacokinetic study
doi.org · Source check Jul 25, 2026
Population: Eight healthy male volunteers.
St. John's wort reduced verapamil bioavailability through induction of first-pass CYP3A4 metabolism without reducing jejunal permeability.
Small healthy-volunteer study; clinical treatment-failure frequency was not measured.
Source 2: current national health-service guidance
nhs.uk · Source check Jul 25, 2026
Population: People taking verapamil.
The NHS states that St. John's wort can affect how verapamil works and directs patients to a pharmacist or doctor before taking it.
Does not quantify the effect by product hyperforin content or dose.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Research summary published |
Article revision: 3227f634718d6852
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.