American track star Marion Jones is expected to plead guilty Friday to charges of lying to U.S. government investigators about using performance-enhancing drugs.

U.S news outlets say Jones revealed in a letter to family and friends that she unknowingly took a banned substance, known as "the clear," for two years, beginning in 1999. She says she received it from her former coach, Trevor Graham, who told her it was flaxseed oil, a nutritional supplement.

Jones says she lied to investigators because she panicked, and wanted to protect herself and Graham.

Her admission ends several years of denials that she had taken performance-enhancing drugs, and could cost her the three gold and two bronze medals she won at the 2000 Olympic Games in Sydney, Australia.

The allegations surfaced after she was linked to a federal steroids investigation involving BALCO, a San Francisco-area laboratory. Several other athletes have been linked to the probe, including Barry Bonds, Major League Baseball's new home run record holder.

Jones will also plead guilty Friday to lying to federal agents about an unrelated check fraud involving former American track star Tim Montgomery, her former boyfriend and father of her oldest child.

"The Washington Post" says she told her family in the letter that she faced up to six months in jail and would be sentenced to three months.

Graham, her former coach, was indicted last November, on three counts of lying to federal agents connected to the BALCO investigation. He has pleaded not guilty, and his trial is scheduled for next month.