Many factors can affect liver metabolism. In aging the numbers of hepatocytes and enzyme activity declines. Diseases that reduce hepatic blood flow like heart failure or shock can also reduce the metabolic potential of the liver.
Metabolism could also be altered due to a genetic deficiency of a particular enzyme. Also the use of other drugs as well as dietary and environmental factors can influence liver metabolic function.
For example, Grapefruit juice and the herb St John’s Wort inhibit Cytochrome P450 activity. On the other hand, cigarette smoke and brussel sprouts increase p450 activity. In fact, there are tables available that list numerous drug, dietary and environmental factors that can interfere with these processes.