This event marked Brock Lesnar's return to MMA action after being out for over a year due to diverticulitis . The lead up to the fight was rife with controversy regarding his opponent, Alistair Overeem . In November 2011, both competitors were required by the NSAC to comply with out-of-competition drug testing. Lesnar delivered his sample screen on November 21, while Overeem delivered his on November 23. The screen, however, did not meet the standards of the commission. Overeem submitted a second test through his personal physician – which was also deemed unacceptable – before flying out of the country. Overeem was ultimately given a conditional license for the fight by the committee during a meeting held on December 12, 2011.