Nutritional supplements interact with pharmaceutical medications through multiple mechanisms — including cytochrome P450 enzyme induction or inhibition (St. John's Wort reducing levels of antiretrovirals, oral contraceptives, warfarin, and statins), antiplatelet effects (fish oil, ginkgo, vitamin E adding to aspirin and warfarin anticoagulation), mineral competition for absorption (calcium inhibiting iron and zinc absorption; zinc competing with copper), and additive pharmacological effects (magnesium with blood pressure medications, chromium with diabetes medications).
Role
Supplement-drug interactions represent one of the most clinically significant and most chronically under-reported safety issues in both conventional and integrative medicine — with the majority of patients taking both pharmaceutical medications and nutritional supplements never having discussed the combination with their prescribing physician, and with most physicians having limited education in supplement pharmacology. The person who supplements heavily without disclosure to their prescribing physician — or who assumes that 'natural' supplements cannot interact with medications — is operating with a false safety assumption that has produced documented adverse events and treatment failures in populations taking clinically critical medications.