Potential Drug Interactions with St. John's Wort

The risk for drug interactions is an important reason to ask patients about use of over-the-counter medications and dietary supplements. In this open-label crossover study, U.S. researchers assessed the effect of St. John's wort (Hypericum perforatum) on the 2 most common drug metabolism enzymes -- cytochrome P₄₅₀ (CYP) enzyme subsystems 3A4 and 2D6.

To establish baseline CYP activity, probe substrates for both enzyme systems (alprazolam for CYP 3A4 and dextromethorphan for CYP 2D6) were administered to 12 healthy volunteers (age range, 22-38). After a washout period, subjects received standardized, commercial preparations of St. John's wort (300 mg 3 times daily) for 14 days, followed by another CYP activity assessment. St. John's wort was …