Reagents can be pure organic or inorganic chemicals substances that react with a substance for testing in chemical laboratories (medicine, pharmacy, ..).). In ascending order, the purity of reagents can be divided into four grades: analytical purity, technical purity and chemical purity. There are also reagents that are unique to each object. They have their own names, often the name of the discoverer, such as Fish, Milo or Nexle. Classification by the analytical reactivity to drug activities. This classification divides organic reagents into nine groups.

1) Color complexing agents

2) Salt-forming substances

3) Substances that can form compounds with little solubility.

4) Indicators

5) Absorbent complexing pigments (paints)

6) Reagents that induce organic synthesis in reaction, analytical applications

7) Reagents that can cyclize with metal ions (wall rings can be either covalent or ligand-bonded, or a combination of both).

8) Oxidizing substances

9) Reducer agents