Alex Rodriguez's ban has been cut to 162 games from 211 by arbitrator Fredric Horowitz.
Rodriguez would have to miss the entrie 2014 season and any postseason games this year under the decision.
The three-time American League MVP was given the 211-game penalty on 5th August following Major League Baseball's investigation of the Biogenesis of America anti-aging clinic, which was accused of distributing banned performance-enhancing drugs.
The number of games sadly comes as no surprise, as the deck has been stacked against me from day one
A-Rod was disciplined by commissioner Bud Selig under MLB's drug agreement and its labour contract.
The Major League Baseball Players Association filed a grievance saying the discipline was without "just cause".
"The number of games sadly comes as no surprise, as the deck has been stacked against me from day one," Rodriguez said in a statement.
Horowitz, who became the MLB's independent arbitrator in 2012, heard the case over 12 sessions from Sept. 30 until 20th November.
Technically, he chaired a three-man arbitration panel that included MLB chief operating officer Rob Manfred and union general counsel Dave Prouty.
The 38-year-old Rodriguez could challenge the ruling in federal court, but judges rarely overturn arbitrators' decisions.
Despite the ban, MLB's drug rules allow Rodriguez to participate in spring training and play in exhibition games.