In April this year a post was made to an instagram account apparently belonging to UFC prospect Johnny Walker, who was most recently seen winning a performance of the night bonus for his KO victory over Khalil Rountree Jr. at UFC Argentina, which advertised a performance enhancing drug. The banned product is Mk-677, also known as ibutamoren.
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UFC Middleweight contender Yoel Romero previously tested positive for ibutamoren back in December 2015. The Cuban received a reduced six month suspension for his positive after demonstrating that his positive test was due to supplement contamination.