The 25-year-old Adams played in 29 big league games for the Orioles in 2011 and spent most of last season with Triple-A Norfolk. He was on Baltimore's 40-man roster at the time of the test.
Adams was assigned outright on Sept. 14 to Norfolk, where he hit .224 with four homers, 18 doubles and 20 RBIs in 65 games this year. He was an All-Star two years ago in the Double-A Eastern League.
Since infielder Neifi Perez was suspended twice and outfielder Mike Cameron once for banned stimulants in 2007, the only major league player other than Adams penalized for a stimulant violation was Milwaukee pitcher Mark Rogers in August 2011.
Adams' suspension was announced by the commissioner's office.
There have been five players suspended this year for performance-enhancing drug violations under the big league testing program: San Francisco outfielder Melky Cabrera and pitcher Guillermo Mota; Oakland pitcher Bartolo Colon; Philadelphia infielder Freddy Galvis; and free-agent outfielder Marlon Byrd.