Normally, a drug you consume should undergo four steps – absorption, distribution, metabolism, and elimination – in order to deliver a therapeutic effect. What if the drug gets eliminated via the intestine without reaching the target? P-glycoprotein (P-gp) is a crucial membrane transporter present on the apical surface of the intestine. If the drug entered acts as a substrate for p-glycoprotein, it will be eliminated from the body. This is where doctors prescribe enzyme inhibitors like CYP2C9 with drugs to protect the drug from elimination. If the enzyme activity is good, it is called a normal metabolizer. Here are the two scenarios as to how drug metabolism affects the response in all metabolizer types.