Made from compounds chemically related to nandrolone - often a mere molecule different - the bio-chemists called them "pro-hormones" or nandrolone precursors. Also known by their chemical names of 19-norandrostenediol and 19-norandrostenedione, these were sold commercially as 19-Nor or "Andro". Because of a loophole in the law in the US, where the Food and Drug Agency classifies Andro as a food supplement, they are sold in pill, capsule and powder form with no need for a prescription, part of an ever-growing £7 billion barely regulated global market for such products.

Because of concerns about the drug's widening illicit use, Britain made nandrolone precursors prescription-only drugs from January 1 this year. The chemical difference between nandrolone and the precursors is minimal - the precursors have the same effects on the body, and the metabolites and waste products are the same too.

The beauty of these products for anyone wanting to give their performance a boost is that they are cheap (around £45 for a month's supply) and there's no need for nasty needles. But what made these new forms of nandrolone a true doper's delight was the clearance time - you could sprinkle Andro on your cornflakes one morning, and know that you could pass any drug test just 24 hours later.

When Mark McGwire, the St Louis Cardinals' baseball slugger, revealed that he used Andro in his home-run record-breaking 1998 season, sales in the product in America increased ten-fold.

McGwire was fortunate because Major League Baseball has no ban on Andro. But just because you can buy a drug over-the-counter at a drug store in Florida, or in Spain, or via the internet, does not mean that it is allowed under Olympic rules of competition. It was not long before some of the biggest names in world sport were returning positive drug tests for nandrolone.

From Olympic track champions such as Linford Christie and Dieter Baumann, to Australian Open tennis winner Petr Korda, to World Cup-winning soccer player Christophe Dugarry, all have handed in little pots of piss that have revealed startlingly high levels of nandrolone.

But this is where the war on drugs ends and the battle for the hearts and minds of the public begins. Almost without exception, no top-level competitor testing positive for nandrolone in the past five years has turned around and admitted that they were using new food supplements (it seems most unlikely that any of them was using injectible nandrolone). Some have even said publicly that they never use any form of food supplement. Many claim that the fault lies entirely with the drug-testing system.