China has ordered all pharmaceutical plants to tag medicines that contain stimulants to prevent athletes from mistakenly using banned drugs during the Olympic games, a drug watchdog official said.

Drugstores were told not to sell such medicine without tags that read "athletes cautious" on the package, Wu Zhen, Vice Director of the State Food and Drug Administration, said.

Only approved pharmaceutical plants and wholesalers are allowed to produce and sell protein assimilation preparations and peptide hormones, the official said.

Chinese law also forbids the sales of protein assimilation preparations except insulin or the sales of peptide hormones.

The moves were aimed at a fair and clean environment for the Games, Wu said.

A catalogue of drugs needed during the Olympic Games has been compiled too.

The Beijing Olympics will feature the largest number of doping tests in the history of the Games, according to officials with the Beijing Organizing Committee for the Olympic Games (BOCOG).

Anti-doping requirements have been issued to all participating athletes at the Beijing Games, the officials said.