The IOC said Bilonog and Krivelyova tested positive for oxandrolone, while the samples from Tsikhan and Yatchenko were positive for methandienone.
Bilonog's disqualification means that both shot put winners in Athens have now been disqualified for doping: Women's champion Irina Korzhanenko of Russia was stripped of gold at the games after testing positive for stanozolol.
In what had been intended as a symbolic and uplifting return to the birthplace of the Olympics, the IAAF held the 2004 shot put competition in Ancient Olympia. The event has now been tarnished by the two drug scandals.
In the men's event, Nelson and Bilonog finished with the same best throw, but the Ukrainian was declared the winner because his second-best attempt was longer. It was the first time an Olympic field event was decided by a second-best mark.
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