When drugs are absorbed by the human body, the molecular size and structure, the permeability of the gastrointestinal membrane, etc. affect the degree and rate of absorption. After absorption, it is transported from the blood to various tissues and organs. The study of the distribution in the body helps to understand the dosage and form of the drug. Afterward, the drug is metabolized by the body, and common types of reactions are oxidation, hydrolysis, reduction, and conjugation. The ultimate goal of metabolism is to facilitate the excretion of drugs from the body, otherwise, accumulation of the drug in the blood will lead to toxicity.