According to Douwe de Boer, former head of the Dutch anti-doping laboratory - who has supported Contador's defence - other cases with higher amounts of the drug have not been prosecuted.

BBC: Ban on clenbuterol doping drug may be relaxed

"There are so many small businesses in Asia that are professional in dealing with buyers but can't afford the software necessary to link up with the networks of large buyers overseas, " says Douwe Cramer, president of Global Sources' e-commerce division.

CNN: Grandaddy of Them All