Toronto Maple Leafs forward Carter Ashton has been suspended for 20 games for violating the terms of the NHL and NHL Players' Association's drug policy.

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.