What kind of interaction is it?

Conflict: combining the two is generally not recommended without clinician oversight.

Is this interaction backed by published research?

Yes. NutriStack lists 3 citation rows for the Erythromycin + St. John's Wort pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·a conflict·Moderate evidence

Erythromycin + St. John's Wort

Q: Can I take Erythromycin and St. John's Wort together?

Generally not recommended together. Erythromycin and St. John's Wort have a documented conflict. St. John's Wort is a potent inducer of CYP3A4 and intestinal P-glycoprotein. Erythromycin is metabolized by CYP3A4 and is a P-gp substrate, so concomitant use can lower erythromycin plasma concentrations and may reduce antibacterial efficacy, risking treatment failure.

Q: How does this affect a NutriStack Stack Score?

-10 to your Stack Score per scored conflict row.

Conflict Moderate evidence

St. John's Wort is a potent inducer of CYP3A4 and intestinal P-glycoprotein. Erythromycin is metabolized by CYP3A4 and is a P-gp substrate, so concomitant use can lower erythromycin plasma concentrations and may reduce antibacterial efficacy, risking treatment failure.

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

Erythromycin and St. John's Wort

Pair type

Conflict, Caution

Evidence

Moderate

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

ConflictModerate evidence

What is happening. St. John's Wort is a potent inducer of CYP3A4 and intestinal P-glycoprotein. Erythromycin is metabolized by CYP3A4 and is a P-gp substrate, so concomitant use can lower erythromycin plasma concentrations and may reduce antibacterial efficacy, risking treatment failure.

Mechanism. Induction of CYP3A4 and P-glycoprotein by hyperforin increases erythromycin clearance and reduces systemic exposure.

Recommendation. Avoid combining St. John's Wort with a course of erythromycin. If an antidepressant or mood supplement is needed, discuss alternatives with the prescriber. Effects of enzyme induction can persist for 1 to 2 weeks after stopping St. John's Wort.

CautionModerate evidence

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

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

Recommendation. Avoid starting or stopping St. John's Wort without prescriber review while taking Erythromycin.

Stack Score

How it moves the number.

Effect on the composite score

If both Erythromycin 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 at /methodology/stack-score.

Sources

Sources, by evidence tier.

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

Reference material

1Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: an updated systematic review. Drugs. 2009.Needs sourceNo link
2Markowitz JS, et al. Effect of St John's Wort on drug metabolism by induction of cytochrome P450 3A4 enzyme. JAMA. 2003.Needs sourceNo link
3Zhou S, et al. Pharmacokinetic interactions of drugs with St John's wort. Journal of Psychopharmacology. 2004.Needs sourceNo link

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