NutriStack
Diltiazem and Quercetin, a caution.
Quercetin pretreatment in rabbits roughly doubled the oral bioavailability of diltiazem by inhibiting CYP3A4 and intestinal P-glycoprotein. While human data are limited, large-dose quercetin supplements (500-1000 mg/day) are plausibly able to raise diltiazem levels and accentuate bradycardia, hypotension, or AV-nodal blockade.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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What the row says.
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At a glance
- Pair type
- Caution
- Evidence (highest tier)
- Emerging
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Emerging evidence
Caution
What is happening. Quercetin pretreatment in rabbits roughly doubled the oral bioavailability of diltiazem by inhibiting CYP3A4 and intestinal P-glycoprotein. While human data are limited, large-dose quercetin supplements (500-1000 mg/day) are plausibly able to raise diltiazem levels and accentuate bradycardia, hypotension, or AV-nodal blockade.
Mechanism. Quercetin inhibits CYP3A4 (the primary diltiazem metabolizing enzyme) and intestinal P-gp, raising oral bioavailability and slowing first-pass metabolism.
Recommendation. Avoid high-dose quercetin supplements while on diltiazem. If you use quercetin, keep doses modest (under 500 mg/day), separate from diltiazem by at least 4 hours, and monitor pulse and blood pressure for 2 weeks.
Minimum separation. 240
Sources (2)
- Choi JS, Li X. Enhanced diltiazem bioavailability after oral administration of diltiazem with quercetin to rabbits. Int J Pharm. 2005;297(1-2):1-8. PMID 15907592
- Mills TA, Kawji MM, Cataldo VD, et al. Profound sinus bradycardia due to diltiazem, verapamil, and/or beta-adrenergic blocking drugs. J La State Med Soc. 2004;156(6):327-31. PMID 15688675
Stack Score
How this pair moves the number.
Effect on the composite score
If both Diltiazem and Quercetin are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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