The medicine that cannot be prepared by purification method is cinnabar.

About the naming of drugs:

Knowledge of how drugs are named can help explain the creation of drug trademarks. Each proprietary drug has at least 3 names: chemical name, common name (non-proprietary drug), and trade name (patented or brand name drug).

A drug's chemical name describes the drug's atomic or molecular structure. Except for some simple inorganic drugs such as sodium carbonate, chemical names are rarely used for general drugs, because although it accurately reflects the chemical structure of the drug, the actual use of chemical names is very complicated and troublesome.

In the United States, drug nonexclusive names are determined by the official organization, the United States Committee on Nomenclature (USAN). Trade names are chosen by pharmaceutical companies. Pharmaceutical companies always choose unique, short, and easy-to-remember trade names to make it easier for doctors to prescribe and for consumers to order by name. For these purposes, the trade name is sometimes related to the use of the drug, such as Diabinese (trade name for chlorpropamide) for treating diabetes and Flexeril (trade name for triiodoquat) for relieving muscle spasms.

FDA requires that the common preparation of a drug should contain the same active ingredients as the original drug and be able to enter the body at the same absorption rate. Whether manufacturers of generic drugs use trade names depends on whether it will increase sales.