Ashton says he unknowingly ingested prohibited substance Clenbuterol through an inhaler used to treat asthma.
"...At no time was I seeking to gain an athletic advantage or to knowingly violate the terms of the program," Ashton said in a statement. "I used the inhaler in response to exercise-induced asthma, a condition that my doctor with the Toronto Maple Leafs has since diagnosed and he has prescribed me with an inhaler.
"As a professional hockey player, I recognize that I am responsible for what I put into my body, and I will not appeal my suspension. While I am extremely disappointed that I have let my teammates, our fans and the Maple Leafs organization down, I will work very hard during my suspension to stay in game shape so that I can help out the team when I am able to return."
Under the terms of the Collective Bargaining Agreement, the suspension is accompanied by mandatory referral to the NHL/NHLPA substance abuse and behavioural health program.
Ashton will forfeit US$169,185 based on his annual salary.
Ashton has played three games for the Maple Leafs this year and has not registered a point.
He has 16 goals and seven assists in 24 games with the American Hockey League's Toronto Marlies.
"The Toronto Maple Leafs support the NHL/NHLPA Performance Enhancing Substances Program and today's decision to suspend forward Carter Ashton," Maple Leafs president Brendan Shanahan said in a statement. "At this time, out of respect for Carter and the process involved, the club will not comment any further."
Ashton is the third player to be suspended under the NHL/NHLPA policy, following Sean Hill in 2007 and Zenon Konopka in May of this year.