Castillo is being banned for using erythropoietin (EPO), a performance-enhancing substance.
"I was recently notified by Major League Baseball that I had tested positive for EPO, a substance that is prohibited under MLB's Joint Drug Agreement," said Castillo via statement. "The positive test resulted from an extremely poor decision that I, and I alone, made. I take full responsibility for my conduct. I have let many people down, including my family, my teammates, the White Sox organization and its fans, and from my heart, I apologize. Following my suspension, I look forward to rejoining my teammates and doing whatever I can to help the White Sox win."
Castillo, 31, from the Dominican Republic, is hitting .270 with 6 home runs and 15 RBIs for the White Sox this season. He was behind the plate for Wednesday's 11-1 win over the Orioles, going 1-for-5 at the plate.
"The Chicago White Sox were saddened and disappointed to learn of the suspension of catcher Welington Castillo for violating Major League Baseball's Joint Drug Prevention and Treatment Program," read a statement from White Sox GM Rick Hahn. "Welington has apologized to the team and his teammates and has taken full responsibility for his actions. He understands that he has negatively affected the team and has fallen short of the expectations we have of our players. The White Sox fully support Major League Baseball's policy and its efforts to eliminate performance enhancing substances from our game."
It's the second notable MLB drug violation this month. Seattle Mariners second baseman Robinson Cano received an 80-game ban after testing positive for furosemide, a diuretic that is not a performance-enhancing drug but is viewed as a masking agent and is on MLB's banned-substance list.