Patton told The Baltimore Sun that he took an Adderall pill four days before the season finished, trying to improve his short-term focus.
"I took one because I was stupid," Patton told the Sun. "It was the end of the season. It was just a stupid mistake."
"I don't have trouble focusing all the time, it just enhances focus in certain situations, and I was just tired, basically. I don't want to list that as an excuse. I know I took a banned substance. It was just a poor lapse in judgment," he said.
The 28-year-old left-hander, a veteran of five major league seasons, was 2-0 with a 3.70 ERA this year in 56 relief appearances.
Under the drug agreement between MLB and its players' union, 25 games is the penalty for a second positive amphetamine test. A first positive results only in follow-up testing.
Patton said he also tested positive for Adderall during spring training in 2010.
Patton became the 15th player suspended this year under the big league drug program following 14 penalized as a result on MLB's Biogenesis investigation.
Orioles executive vice president of baseball operations Dan Duquette said the team was "disappointed to learn of Troy Patton's suspension."
MLB permits an exemption for players with attention deficit disorder, but Patton told the Sun he'd never been diagnosed with the condition. He said he tried to apply an exemption in 2012, but was turned down after doctors examined him.
The annual report from the drug program's independent administrator, Dr. Jeffrey M. Anderson, said 119 therapeutic use exemptions were granted for ADHD drugs in the year ending with the conclusion of the World Series. There were seven positive tests for Adderall in that span.