NutriStack
Sildenafil and St. John's Wort, a conflict.
St. John's Wort induces CYP3A4, the primary enzyme metabolizing sildenafil. This can reduce sildenafil effectiveness.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Sildenafil and St. John's Wort
- Pair type
- Conflict
- Evidence (highest tier)
- Moderate
- Source citations
- 1 source
- Stack Score effect
- −10 to your Stack Score (per scored conflict row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Conflict · Moderate evidence
Conflict
What is happening. St. John's Wort induces CYP3A4, the primary enzyme metabolizing sildenafil. This can reduce sildenafil effectiveness.
Mechanism. Sildenafil is metabolized by CYP3A4 (major) and CYP2C9 (minor). CYP3A4 induction by SJW increases sildenafil clearance, reducing its duration and peak effect.
Recommendation. Avoid SJW with sildenafil as it may reduce its effectiveness.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Sildenafil and St. John's Wort are in the same stack, this pair applies −10 to your Stack Score (per scored conflict row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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