What kind of interaction is it?

Caution: an interaction that may reduce efficacy or raise side-effect risk and warrants monitoring.

Is this interaction backed by published research?

Yes. NutriStack lists 1 citation row for the Famciclovir + Quercetin pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·a caution·Insufficient evidence

Famciclovir + Quercetin

Q: Can I take Famciclovir and Quercetin together?

Possibly, but with caution. Famciclovir and Quercetin have a documented caution-tier interaction. Famciclovir is an inactive prodrug that must be converted to its active form, penciclovir, largely by the enzyme aldehyde oxidase. Quercetin inhibits aldehyde oxidase in laboratory studies, which raises a theoretical possibility that high-dose quercetin could slow the activation of famciclovir and modestly reduce active drug formation. Human data confirming a clinically meaningful effect are lacking.

Q: How does this affect a NutriStack Stack Score?

-5 to your Stack Score per scored caution row.

Caution Insufficient evidence

Famciclovir is an inactive prodrug that must be converted to its active form, penciclovir, largely by the enzyme aldehyde oxidase. Quercetin inhibits aldehyde oxidase in laboratory studies, which raises a theoretical possibility that high-dose quercetin could slow the activation of famciclovir and modestly reduce active drug formation. Human data confirming a clinically meaningful effect are lacking.

Supplement × Prescription

Open the interaction checker → Read the methodology

From the database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, and the recommendation.

Substances

Famciclovir and Quercetin

Pair type

Caution

Evidence

Insufficient

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

CautionInsufficient evidence

What is happening. Famciclovir is an inactive prodrug that must be converted to its active form, penciclovir, largely by the enzyme aldehyde oxidase. Quercetin inhibits aldehyde oxidase in laboratory studies, which raises a theoretical possibility that high-dose quercetin could slow the activation of famciclovir and modestly reduce active drug formation. Human data confirming a clinically meaningful effect are lacking.

Mechanism. Aldehyde oxidase oxidizes 6-deoxypenciclovir to penciclovir during first-pass activation of famciclovir. Quercetin is a known in vitro inhibitor of aldehyde oxidase, so substantial inhibition could in theory lower conversion to the active antiviral, reducing exposure to penciclovir.

Recommendation. No change to standard famciclovir dosing is required for typical dietary quercetin. If using high-dose quercetin supplements during a short antiviral course, complete the full famciclovir course as prescribed and report any apparent lack of response to your clinician. Separating doses is not necessary.

Stack Score

How it moves the number.

Effect on the composite score

If both Famciclovir 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 at /methodology/stack-score.

Sources

Sources, by evidence tier.

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

Reference material

1Barr JT, Jones JP. Inhibition of human aldehyde oxidase: implications for drug metabolism and drug-drug interactions. Drug Metab Dispos. 2011.Needs sourceNo link

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