Grandal's suspension will be effective at the start of the 2013 season.
"I apologize to the fans, my teammates, and to the San Diego Padres," Grandal said in a statement. "I was disappointed to learn of my positive test and under the Joint Drug Program, I am responsible for what I put into my body. I must accept responsibility for my actions and serve my suspension."
Grandal, 23, made his Major League debut for the Padres on June 2 and hit .297 with eight home runs and 36 RBIs in 192 at-bats. In his first start, he hit two home runs against the Rockies on June 30.
"We were disappointed to learn of the suspension of Yasmani Grandal for violating Major League Baseball's Joint Drug Prevention and Treatment Program. We fully support Major League Baseball's policy and its efforts to eliminate performance-enhancing drugs from our game. Per the protocol outlined by Major League Baseball's Collective Bargaining Agreement, we will not comment further on this matter," the Padres said in a prepared statement.
Grandal was one of four players the Padres acquired from the Reds last December in the deal that sent pitcher Mat Latos to the Reds. He was a first-round Draft pick in 2010 (12th overall) by the Reds out of the University of Miami.
Grandal started the season with Triple-A Tucson and hit .323 with six home runs and 35 RBIs in 201 at-bats. He was promoted to the big leagues on June 1 and returned two days later. Grandal later joined the Padres for good on June 30.
All told, Grandal appeared in 55 games last season and started 52 of them. In addition to Grandal, the Padres have two other catchers on the 40-man roster -- John Baker and 2012 Opening Day starter, Nick Hundley.
At the General Manager Meetings on Wednesday, Padres general manager Josh Byrnes said the team is still sorting through the suspension and exactly what it will prohibit Grandal from doing once the regular season begins.
"It works well with extended [spring camp]. He can play there. The competition isn't great, but at least he can play there. We'll see," Byrnes said. "I actually have to learn what he can do as far as playing in Minor League games. I'll see whether it's 50 some games or we can expect to see him in the 51st game. I'm not exactly sure."
Grandal won't be eligible to play until May 28 when the Padres face the Mariners in Seattle.