API can be divided into two categories: chemical synthetic medicine and natural chemical medicine according to its source.

Chemical synthetic drugs can also 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 to treat gastric and duodenal ulcers; Organic synthetic drugs are mainly drugs made from basic organic chemical raw materials through a series of organic chemical reactions (such as aspirin, chloramphenicol, caffeine, etc.).

Natural chemical drugs can also be divided into biochemical drugs and phytochemical drugs according to their sources. Antibiotics are generally produced by microbial fermentation, belonging to the category of biochemistry. In recent years, a variety of semi synthetic antibiotics are the combination of biological synthesis and chemical synthesis. Among the bulk drugs, the varieties, output and output value of organic synthetic drugs account for the largest proportion and are the main pillar of the chemical pharmaceutical industry. The quality of APIs determines the quality of preparations, so its quality standards are very strict. Countries around the world have formulated strict national pharmacopoeia standards and quality control methods for APIs that are widely used.