Drug elimination in the body refers to the process of continuous elimination of a drug through distribution, metabolism and excretion after it enters the blood circulation in the body. The main method of drug elimination is the metabolism of drugs in the body. Drug metabolism refers to the drug into the body under the action of a variety of metabolic enzymes, the chemical structure of the drug changes in the process, also known as the biological transformation of drugs. The biotransformation and excretion of drugs are collectively known as drug elimination. There are four types of drug metabolism which are reduction, oxidation, conjugation and hydrolysis. Drugs are metabolized mainly by both hepatic and intestinal wall, where the P450 enzyme system plays a large role in hepatic metabolism, while intestinal wall metabolism is only a small part of the drug metabolism. Drug metabolism in the body usually has two endings: one is the inactivation of the drug, that is, it becomes pharmacologically inactive; the other result is activation, which can be changed from a pharmacologically inactive drug to a pharmacologically active metabolite, or the metabolism still maintains the original pharmacological effect, or it can produce poisonous substances, and it also suggests that the biological metabolism may not be a detoxification process as well.