According to its source, API is divided into two categories: chemical synthetic drugs and natural chemical drugs.

Chemical synthetic drugs can be divided into inorganic synthetic drugs and organic synthetic drugs. Inorganic synthetic drugs are inorganic compounds (very few are elements), such as aluminum hydroxide and magnesium trisilicate, used for treating gastric and duodenal ulcers; Organic synthetic drugs are mainly drugs made from basic organic chemical materials through a series of organic chemical reactions (such as aspirin, chloramphenicol, caffeine, etc.).

According to their sources, natural chemical drugs can also be divided into biochemical drugs and phytochemical drugs. Antibiotics are generally produced by microbial fermentation and belong to the biochemical category. In recent years, a variety of semi-synthetic antibiotics are the combination of biosynthesis and chemical synthesis. Among the bulk drugs, organic synthetic drugs account for the largest proportion in variety, yield and output value, and are the main pillar of the chemical pharmaceutical industry. The quality of API determines the quality of the preparation, so its quality standards are very strict. All countries in the world have formulated strict national pharmacopoeia standards and quality control methods for its widely used API.