BEIJING, June 29 (Xinhua) -- China's drug watchdog is to inspect all drugstores and medical retail companies across the country, with a focus on Olympic venues of Beijing and the eastern province of Shandong, to root out performance-enhancing drugs.

"Drug supervision agencies must tighten inspections to ensure that banned doping substances are not sold," the State Food and Drug Administration said in a circular.

It requires all drugstores to post clear signs, reading "The sale of peptide hormones and protein assimilation preparations (insulin excluded) is prohibited", and drugs containing banned substances listed in the doping catalogue must carrying warnings for athletes on labels or in instructions.

"We must be alert to the performance enhancing drugs to create an environment of fair competition for the 2008 Beijing Olympic Games," the circular says.