Does Grapefruit Affect St. John's Wort?

Use extra care with this combination

The short answer

St. John's Wort induces CYP3A4 while grapefruit inhibits it. The opposing and unpredictable effects on drug/supplement metabolism create dangerous variability in blood levels.

How to arrange timing

Avoid combining grapefruit with St. John's Wort. The unpredictable CYP3A4 effects are dangerous.

Reference

Reference noted for this food and supplement combination: FDA; Markowitz et al., Clin Pharmacol Ther 2003

Important context

The effect can also change with food amount, supplement dose, product formulation, health conditions, and medication use. Ask a doctor or pharmacist first if you take medication, are pregnant or breastfeeding, or have a chronic condition.