The Office of the Commission of Baseball issued a statement saying Colon tested positive for testosterone.
Colon, 39, is 10-9 this season with a 3.43 earned run average. The win total and ERA are team bests this season. The 10 wins in a season are the most for Colon since he won 21 games in 2005, when he was voted the American League Cy Young Award.
Oakland team officials issued a statement that they were "disappointed" to learn of Colon's suspension but that they supported baseball's drug policy.
Colon is the second player to be suspended for performance-enhancing substance violations in a week. San Francisco outfielder Melky Cabrera was banned for 50 games. His test was also positive for testosterone.