Shamrock tested positive for 9-Norandrosterone, 19-Noretiocholanolone and Stanozolol and has been fined $2,500 and suspended through February 1, 2010.
Shamrock (27-13-2) at "Valentine's Eve Massacre" won for the first time since June 2004, submitting 350-plus-pounder Ross Clifton with an armbar.
Shamrock is scheduled to fight former WWE pro wrestler Bobby Lashley on March 21 at the "March Badness" MMA/boxing event headlined by Roy Jones Jr. vs. Omar Sheika.
Shamrock has the right to appeal but will not be able to in time for the fight.
That will be the second straight high-profile fight Shamrock has been forced out of. Last October at EliteXC "Heat," Shamrock pulled out the same day of the fight due to a cut suffered while warming up.
Shamrock was also looking forward to a fight against fellow UFC old schooler Tank Abbott at the next WarGods-KSP event to take place in Reno, Nevada.