Major League Baseball made the announcement Wednesday, one week after All-Star game MVP Melky Cabrera of San Francisco was suspended 50 games for a positive test for the same substance.
"I apologize to the fans, to my teammates and to the Oakland A's," Colon said in a statement released by the players' association. "I accept responsibility for my actions and I will serve my suspension as required by the joint drug program."
He will miss the final 40 games of the regular season and the first 10 games of the postseason if Oakland advances that far. Any remainder of the suspension would be served in a future season, if Colon signs another major league contract.
"It's a shock," Oakland reliever Grant Balfour said. "He's a guy that we're definitely relying on right now. I guess you could say it's bad timing any time, but especially now."
Oakland, which hasn't made the playoffs since 2006, began Wednesday a half-game out in the AL wild-card race.
The 39-year-old pitcher is 10-9 with a 3.43 ERA in 24 starts this season, his first with the A's, and has a 171-122 record in 15 big league seasons. A two-time All-Star, he won the 2005 AL Cy Young Award after going 21-8 for the Los Angeles Angels.
Colon will lose the remaining $469,945 of his $2 million base salary this year. He also has earned $600,000 in performance bonuses based on starts, which is not impacted.
Five players have been suspended this year under the big league drug program. San Francisco reliever Guillermo Mota was penalized 100 games in May following his second positive test, and Philadelphia infielder Freddy Galvis and free agent outfielder Marlon Byrd were suspended 50 games each in June.