Almost 20 percent of dietary supplements bought in Britain as part of a study contained substances which would lead to an athlete failing a doping test, the International Olympic Committee announced today.
The medical commission of the IOC examined 634 non-hormonal nutritional supplements bought in 13 countries between October 2000 and November 2001.
Of these, 94 were found to contain substances not listed on the label and which would have led to a positive doping test and ban for an athlete, the IOC said.
Among substances found were nandrolone, the banned steroid for which British track stars Linford Christie, Dougie Walker and Mark Richardson have all tested positive.
A total of 37 products were bought in Britain and tested, of which seven, or 18.9 percent, would have resulted in a positive test result.
Of the 94 samples which contained substances of concern, 23 had precursors of both nandrolone and testosterone.
Ron Maughan, professor of physiology at Aberdeen University, said despite traces of both being small, the fact they were even found is of grave concern.
"It is hugely worrying if you are an athlete subject to drug testing because your career could be terminated," he said.
"I think it is of a great concern that you can have something that is not listed on the packet but is a powerful drug and you can buy it off the shelf.
"There is no significant risk to health from things like nandrolone and testosterone in small amounts. The problem comes with large amounts over time.
"It can lead to major mood swings, depression, an increase in coronary problems, and a significant risk of liver disorder and liver tumours."
An IOC statement said: "While the IOC has issued its warnings to elite athletes and their entourages, especially due to their liability under doping control tests, the fact that the public is unknowingly ingesting the precursors to hormones should be a matter of public health concern."
The IOC said the findings demonstrated the need for greater quality control to ensure substances not on the label are not in the product.