A 27-page CAS ruling dated May 2, 2014 and obtained by Reuters indicated that the 27-year-old 400 metres runner is now suspended for "four years and six months", with the ban backdated to July 1, 2012.
The reduction to her suspension means Blake will able to resume her career at the end of January 2017.
The Jamaica Anti-Doping Disciplinary Panel handed Blake the six-year suspension on June 13, 2013, starting on that date, after she tested positive for the banned stimulant methylhexanamine at the previous year's Olympic trials.
However, a CAS panel sided with Blake's appeal for a reduced period of ineligibility, which was filed by her legal team.
"The panel would allow Ms Blake's appeal to the extent that the six-year period of ineligibility imposed by the decision should be reduced to four years and six months. The starting date for the term of ineligibility is July 1, 2012," read the ruling.
Blake, who previously served a nine-month suspension after testing positive for ephedrine in 2006, finished sixth at the Jamaican trials and was selected on the relay team for the London Olympics but did not compete at the Games.
Jamaica's women won the bronze medal in London after they finished third in the 4x400m relay final.
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