Slice and Shamrock had banned substances in their system per the results of pre-fight drug tests, multiple sources said. Bellator 149 took place Feb. 19 in Houston, Texas.
Both men have been administratively suspended by the Texas Department of Licensing and Regulation (TDLR) pending an adjudication process, sources said. The official test result documents, showing the exact substances Slice and Shamrock tested positive for, have been withheld by the TDLR due to potential pending litigation. Athletes on the card had urine samples taken before their bouts.
Typically, the maximum discipline for combatants who fail drug tests in Texas is a 90-day suspension and $5,000 fine.
Shamrock also failed a drug test in California in 2009 after a win over Ross Clifton at WarGods: Valentine's Eve Massacre. At the time, three steroids were found in Shamrock's system: norandrosterone, noretiocholanolone and stanozolol.
When reached by MMA Fighting, Texas Combative Sports Program director Greg Alvarez had no comment, referring all inquiries to open records officials.
Bellator spokesman Danny Brener said the promotion had not been officially notified of any test failures and, because of that, cannot comment. Brener added that Bellator MMA president Scott Coker is looking into the matter.
MMA Fighting reached out to representatives of both Shamrock and Slice, but did not receive a response as of Friday afternoon.
Royce Gracie defeated Ken Shamrock via first-round TKO in the main event of Bellator 149. Gracie appeared to land a low blow with his knee in a clinch, which led to Shamrock being dropped and ultimately finished. Shamrock was appealing the result, but that is likely out the window with his positive drug test.
In the co-main event, Slice, whose real name is Kevin Ferguson, defeated Dada 5000 by third-round TKO. That bout has been officially overturned into a no contest, according to MixedMartialArts.com.
Dada, whose real name is Dhafir Harris, suffered cardiac arrest after that fight, sources told MMA Fighting, and had to be resuscitated. He was released from the hospital last week.
Shamrock, 52, was making his second appearance in Bellator after coming out of retirement last year. His fight against Slice, a first-round knockout loss, in June 2015 was his first bout since 2010. Shamrock is a legend in MMA, a UFC Hall of Famer and fought at UFC 1.
Slice, 42, returned to MMA against Shamrock last year after five years away. The Miami native has a massive following, stemming from his streetfighting videos going viral on YouTube. He is also a UFC veteran with an appearance on The Ultimate Fighter 10.
Bellator 149 was the highest rated show in promotion history, drawing an average of more than 1.9 million viewers. The bout between Slice and Dada 5000 averaged 2.5 million viewers, while Gracie vs. Shamrock averaged 2.4 million.