Antonio Pettigrew testified at the trial of coach Trevor Graham that he had taken banned drugs since the 1996 US trials. His confession followed drugs bans on Alvin and Calvin Harrison and Jerome Young who were also members of the victorious US team.
"I know that the medal was not fairly won and that it is dirty," Johnson said in a column published in The Daily Telegraph on Tuesday.
"So difficult as it is, I will be returning it to the International Olympic Committee because I don't want it. I feel cheated, betrayed and let down."
Graham was convicted last Thursday on one count of lying to federal agents investigating the BALCO laboratory.