Athletes warned off food supplements

Mark Richardson blamed supplements for his ban

Athletes have been warned again against using food supplements after an IOC study confirmed that up to 20% contained banned drugs.

"The first extensive reports on 600 nutritional supplements show that some contain non-labelled substances which could lead to a positive doping test," the International Olympic Committee said in a statement.

"At this stage, the IOC Medical Commission can only recommend to athletes and their entourage not to take such products," it said.

The percentage figures confirmed those revealed by the IOC eight days ago after a third of the 600 food supplements had been analysed by testers in Cologne, Germany.

The IOC has been warning athletes against using supplements for some time.

In the last few years, several athletes who tested positive for such substances as the anabolic steroid nandrolone have blamed the test results on the products.

The IOC hopes to be able to finish its investigation within the next year.