The 37-year-old British Columbia native was in his first season with the Ducks, registering 10 points in 45 games. The suspension is without pay and Horcoff is automatically referred to the NHL and NHL Players' Association joint program for substance abuse and behavioral health.
The suspension will cost Horcoff $357,526.88.
"While recovering from an injury I suffered this past fall, I tried a treatment that I believed would help speed up the healing process," Horcoff said in a statement. "Although I was unaware that this treatment was not permitted under NHL rules, that is no excuse whatsoever. I should have done my research and I should have checked with the NHL/NHLPA Performance Enhancing Substances Program's doctors. I accept full responsibility for my actions, and I am sorry.
"Throughout my entire career, I have felt genuinely blessed and honored to the play the great game of hockey, and I regret the impact that this may have on my team and our fans. I look forward to the day I return to the ice for the playoff push."
Ducks coach Bruce Boudreau said Tuesday night that while "everybody was shocked by it," Horcoff is their teammate and they support him. Boudreau added that they support the testing.
Ducks general manager Bob Murray also issued a statement Tuesday on the suspension.
"This morning we were made aware of the situation regarding Shawn Horcoff," he said. "The Anaheim Ducks organization fully supports the NHL/NHLPA Performance Enhancing Substances Program. We will also continue to support Shawn as a player and person throughout this process. We will have no further comment at this time."
Before arriving in Anaheim, Horcoff spent two seasons in Dallas. He played 12 years in Edmonton, serving as captain from 2010 to '13.
The NHL doesn't have a long history of PED suspensions. Toronto's Carter Ashton was suspended 20 games in 2014 for using a banned drug called clenbuterol. At the time, he was the third NHL player to be suspended under the program. Ashton said his suspension was the result of using the inhaler of another athlete he was training with.
That same year, Sabres forward Zenon Konopka was suspended 20 games for testing positive for a banned substance. Konopka said he ingested a product purchased over the counter and didn't realize it contained a banned substance.
Before Konopka, only Sean Hill was suspended for PEDs, with his 20-game ban coming in 2007.