Supplement × Prescription·contraindicated·Moderate evidence

St. John's Wort + Voriconazole

Contraindicated Moderate evidence

St. John's Wort can induce drug-metabolizing enzymes and transporters and may lower Voriconazole exposure or undermine therapy.

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Pair type
Contraindicated
Evidence
Moderate
Source citations
1
Scope
Supplement × Prescription
Last verified
June 4, 2026
ContraindicatedModerate evidence

What is happening. St. John's Wort can induce drug-metabolizing enzymes and transporters and may lower Voriconazole exposure or undermine therapy.

Mechanism. Hyperforin induces CYP3A4 and P-glycoprotein, which can reduce exposure to susceptible drugs.

Recommendation. Avoid St. John's Wort with Voriconazole.

Stack Score

How it moves the number.

Effect on the composite score

If both St. John's Wort and Voriconazole are in the same stack, this pair applies −25 to your Stack Score (per scored contraindication row).

The full algorithm, the clamping rules, and four worked stacks are at /methodology/stack-score.

Sources

Sources, by evidence tier.

Every claim on this page is cited. PMIDs link straight to PubMed.

Reference material

1
  • 1Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: an updated systematic review. Drugs. 2009.Needs sourceNo link

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