Before a three-member panel of the Jamaica Anti-Doping Commission, the Olympic 4x100-relay gold and silver medalist insisted she was not a "cheat."
She testified that she believed a supplement provided by trainer Christopher Xuereb of Canada was responsible for her positive test.
Simpson, along with former 100-meter world record holder Asafa Powell, tested positive for the stimulant oxilofrone at the sprinting powerhouse's national championships in June.
At Jamaica's June championships, Simpson said she was still being bothered by a nagging hamstring injury but was in "fairly good shape." She had just recently begun working with Xuereb, a trainer who she testified she first spoke to on May 16 and worked with at Powell's house in Kingston on the same day.
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"I trusted Chris," she told the panel. "I invited Chris into my very small circle."
Simpson said that one of six supplements provided by Xuereb was responsible for her "devastating" positive test. She said she researched the "Epiphany D1" supplement for up to 14 hours online before starting to take it and "nothing I read raised a red flag or an alarm bell."
Xuereb has said he didn't give Simpson and Powell any performance-enhancing drugs and only purchased major brand vitamins.