UFC 150 took place on Aug. 11th at Pepsi Center in Denver, Colo. Shields, 35, fought and defeated Herman via unanimous decision.
Shields did not specify which substance he took that resulted in the suspension. The Colorado Boxing Commission does also not disclose test results according to their own state laws.
"Prior to my professional bout at UFC 150 in Denver, Colorado, I used a substance prohibited by Colorado Boxing Commission rules," Shields said in a statement. "This was a mistake that I fully regret. I have shared this issue with my family and the UFC and I have apologized to them and now I also apologize to you, the fans. I promise this will never occur again in my fighting career. I accept the Boxing Commission's decision for a six-month suspension, which will expire in February. I ask that you accept my apology. I will be back fighting soon, and hope that the fans of MMA will support me until that time."
Prior to this incident, Shields has never tested positive for any performance-enhancing drugs or any other banned substance in his 35-fight professional career.
He previously fought at middleweight early in his career as well as 2009 and 2010 as Strikeforce's middleweight champion. Shields moved back to welterweight and made his UFC debut at UFC 121 in October of 2010 where he defeated Martin Kampmann via unanimous decision. His most-recent return to middleweight began with the fight at UFC 150 against Herman.