American sprinter Bernard Williams tested positive for a metabolite of cannabis at a meeting in Seville in June, but can still compete in Athens.
Bernard Williams won gold in the 4x100m relay in Sydney
Williams, a gold medal winner in the US 4x100m relay team at the Sydney Games, only received a warning despite testing positive for the banned substance.
The US Anti-Doping Agency (USADA) said Williams had committed a first offence.
"He received a public warning, in accordance with the IAAF rules for a first offence," it said.
"In addition, he is disqualified from his second-place
finish in the 200m at the Seville meeting.
"Williams is eligible to compete at the 2004 Olympic Games in Athens."