NutriStack
Amlodipine and St. John's Wort, a conflict.
St. John's Wort is a potent inducer of CYP3A4 via pregnane X receptor (PXR) activation. Amlodipine is primarily metabolized by CYP3A4. Co-administration can significantly reduce amlodipine blood levels, potentially rendering the medication ineffective at controlling blood pressure. The induction effect typically develops over 10-14 days and takes a similar period to resolve after discontinuation.
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
- Amlodipine and St. John's Wort
- Pair type
- Conflict
- Evidence (highest tier)
- Strong
- Source citations
- 2 sources
- Stack Score effect
- −10 to your Stack Score (per scored conflict row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Conflict · Strong evidence
Conflict
What is happening. St. John's Wort is a potent inducer of CYP3A4 via pregnane X receptor (PXR) activation. Amlodipine is primarily metabolized by CYP3A4. Co-administration can significantly reduce amlodipine blood levels, potentially rendering the medication ineffective at controlling blood pressure. The induction effect typically develops over 10-14 days and takes a similar period to resolve after discontinuation.
Mechanism. Hyperforin, the active constituent of St. John's Wort, activates the nuclear pregnane X receptor (PXR), inducing transcription of CYP3A4 and other drug-metabolizing enzymes. This accelerates amlodipine's hepatic and intestinal metabolism, reducing bioavailability and plasma concentrations below therapeutic levels.
Recommendation. Avoid combining St. John's Wort with amlodipine. If currently taking both, consult your prescriber before making changes. Abruptly stopping St. John's Wort could cause amlodipine levels to rise. If blood pressure control is lost, St. John's Wort should be considered as a potential cause.
Sources (2)
- Nicolussi S et al. Clinical relevance of St. John's wort drug interactions revisited. Br J Pharmacol. 2020;177(6):1212-1226. PMID 31742659
- Moore LB et al. St. John's wort induces hepatic drug metabolism through activation of the pregnane X receptor. Proc Natl Acad Sci USA. 2000;97(13):7500-7502. PMID 10852961
Stack Score
How this pair moves the number.
Effect on the composite score
If both Amlodipine 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.
Check your full routine
One pair was the worked example. NutriStack runs every pair in your stack at once.
Drop in your supplements and prescriptions and the public database surfaces every interaction, synergy, timing rule, and contraindication, every one linked to its primary source.