USADA said Cox's punishment "resulted from information recently received by USADA during separate investigations arising from information obtained during the BALCO doping conspiracy."
In addition to her suspension, which began on January 26, "all of Cox's competitive results will be disqualified, including forfeiture of all medals, points, and prizes since November 3, 2001," USADA said.
That almost certainly means she will lose her Olympic gold medal, although the fate of her relay teammates was not immediately known.
"Ms. Cox clearly competed under the pressures of her sport that accompanied one of the worst doping chapters in history and unfortunately gave in to the temptation to use performance-enhancing drugs, USADA chief executive Travis Tygart said.
"However, to her credit, when confronted by USADA with evidence of her violation of sports anti-doping rules Ms. Cox promptly admitted her involvement in doping and accepted responsibility."
The investigation into the Bay Area Laboratory Cooperative, source of the designer steroid THG, rocked the sports world prior to the Athens Olympics, and the fallout has continued in a wide range of sports.
One-time sprint queen Marion Jones served a prison sentence after admitting she perjured herself when she told investigators she didn't use performance enhancing drugs.
Former NFL player Dana Stubblefield received probation on similar perjury charges, while baseball home run king Barry Bonds's trial on perjury charges stemming from the BALCO probe is still pending.
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