Jake Shields accepts suspension

Updated: October 12, 2012, 7:13 PM ET

UFC middleweight Jake Shields has admitted he used an unnamed prohibited substance prior to a win against Ed Herman at UFC 150 in August in Denver.

In a statement released by his management team Friday, Shields announced the Colorado Boxing Commission has served him a six-month suspension, which he will not appeal.

"Prior to my professional bout at UFC 150, I used a substance prohibited by Colorado Boxing Commission rules," Shields said in the statement. "This was a mistake that I fully regret.

"I accept the Boxing Commission's decision for a six-month suspension, which will expire in February. I ask that you accept my apology."

The Colorado Department of Regulatory Agency has not confirmed the suspension on its website. Interim public information officer Cory Everett-Lozano would neither confirm nor deny the presence of an investigation to ESPN.com.

Shields (28-6) returned to the 185-pound weight class against Herman after a four-fight run in the welterweight division.

The former Strikeforce champion is 3-2 since signing with the UFC in 2010. It's unknown whether the win against Herman will be overturned.