Marion Jones admitted using steroids before the 2000 Olympics in a recent letter to close family and friends, The Washington Post reported Thursday.
Jones, who won five medals in Sydney, said she took "the clear" for two years, beginning in 1999, and that she got it from former coach Trevor Graham, who told her it was flaxseed oil, the newspaper reported.
"The clear" is a performance-enhancing drug linked to BALCO, the lab at the center of a federal steroids investigation. Until now, Jones had steadfastly denied she ever took any kind of performance-enhancing drugs.
Jones also said she will plead guilty Friday in New York to two counts of lying to federal agents about her drug use and an unrelated financial matter, the Post reported.
"I want to apologize for all of this," the Post reported, quoting a person who received a copy of the letter and read it to the paper. "I am sorry for disappointing you all in so many ways."
The admission could cost Jones the medals from the Sydney Olympics, where she was one of the United States' brightest stars. Though she fell short of her goal of winning five gold medals, she came away with three and two bronzes.
But her career has been tarnished since then by doping allegations. In her letter, Jones said she lied when she was questioned in 2003 by federal agents investigating the Bay Area Laboratory Co-Operative. Jones said she panicked when agents presented her with a sample of "the clear," which she recognized as the substance Graham had given her.
In the letter, Jones said she didn't realize she'd used a performance-enhancing drug until she stopped training with Graham at the end of 2002.
"Red flags should have been raised when he told me not to tell anyone," the Post reported, quoting the letter.