Major League Baseball announced the suspension on Thursday. Hernandez began serving the penalty immediately. He was on the Class A Peoria roster.
"The Chicago Cubs strongly support the drug prevention and treatment programs set forth by Major League Baseball," said Oneri Fleita, Cubs player development director. "We constantly educate our players to the dangers and consequences of the use of illegal substances and adhere to the programs at all levels of our organization."
Hernandez, 19, a right-hander from Venezuela, was 8-9 with a 4.34 ERA in 20 starts last season at Peoria. He struck out 71 over 103 2/3 innings.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.