Speaker: David Hoffmann. The cytochrome p450 liver enzyme system is a family of related enzymes catalyzing different reactions in the body. This system can be altered by a number of mechanisms and efficiency varies significantly among people, leading to variability of both efficacy and toxicity of drugs. Induction of the CYP450 system increases the rate of biotransfomation, thus decreasing concentrations of the drug and hence its pharmacological effects. Inhibition of p450 enzymes results in increased concentrations of the drug, thus prolonging pharmacologic effects and increasing incidence of drug-induced toxicity. The most significant drug interactions are those involving drugs with narrow therapeutic windows, for example anticoagulants such as warfarin can cause bleeding if the amount of drug is increased as a result of a drug interaction. An ever-growing number of foods and herbs have been found to interact with the CYP450 enzyme system, grapefruit juice is a strong inhibitor, and many substances including red wine, St. Johns wort and cruciferous vegetables are all inducers. The synergistic possibilities for therapeutic benefit. are very real The rest of the lecture describes botanicals which may support detoxification of drugs, prevent cancer through anti-inflammatory effects, and possibly overcome multiple drug resistance in cancer therapeutics, all due to their actions on CYP450 enzymes.