Why bother about cytochrome P450 enzymes?

The cytochrome P450 system is a group of enzymes, found mainly in the liver and gut mucosa, that controls the concentrations of many endogenous substances and drugs. The activity of the individual enzymes can vary over time and from person to person in response to diet, medicines or exposure to environmental pollutants. Here, we review the cytochrome P450 system and consider its relevance to prescribing.