The league announced the ban on Wednesday, confirming that the outfielder had tested positive for an amphetamine.
Maybin, whose suspension will begin immediately, said that his use of the banned substance had been connected to his treatment for Attention Deficit Disorder (ADD), for which he previously had a therapeutic use exemption granted.
"Unfortunately, in my attempts to switch back to a medicine that had been previously okayed, I neglected to follow all the rules and as a result I tested positive," Maybin said in a statement issued by the MLB Players' Association.
Maybin added: "I want to assure everyone that this was a genuine effort to treat my condition and I was not trying in any way to gain an advantage in my baseball career.
"I understand that I must accept responsibility for this mistake and I will take my punishment and will not challenge my suspension.
"I apologise to my family, friends, fans, team-mates, and the entire Padres organisation.
"I look forward to returning to the field and contributing to the success of my club."
After an injury-ravaged season last term, Maybin has batted at .247 for the Padres this year, with one home run and nine RBIs in 62 games.