Drug-herbal Interactions

Components of grapefruit inhibit cytochrome P450 isoenzyme CYP3A4 and increase the plasma level of a number of drugs; for example, it can significantly enhance the anticoagulant effect of warfarin.¹³ Ginkgo biloba inhibits platelet function; its use with acetylsalicylic acid (ASA), other nonsteroidal anti-inflammatory agents (NSAIDs), and clopidogrel, which also interfere with platelet aggregation, increases the risk of bleeding.⁶

St. John’s wort induces the cytochrome P450 isoenzyme CYP3A4 and decreases the efficacy of many drugs, including some prescribed by oral healthcare providers, e.g., benzodiazepines and macrolides antibacterial agents.^12,13 Large doses of vitamin C acidify the urine, inhibit the excretion of weak acids such as NSAIDs, acetaminophen, and tetracyclines (e.g., doxycycline and minocycline) and thus increase the plasma levels of these and other drugs.