Per ESPN:

"I was informed today that I have tested positive for marijuana," Singleton said in the statement. "As a result, I am being suspended for the first 50 games of the 2013 season. I accept the penalty and take full responsibility for my actions. I apologize to my parents, the Houston Astros and [general manager] Jeff Luhnow.
http://espn.go.com/mlb/story/_/id/88...ended-50-games