Silva (15-3) defeated Nedkov via submission in the third round of their co-main event at the UFC on Fuel event in Macau. The decision, however, will be changed to a no-contest due to Silva's suspension.
UFC officials confirmed the light heavyweight's failed drug test and suspension to ESPN.com on Wednesday. Silva also will attend a drug rehab program.
"The UFC organization has a strict, consistent policy against the use of illegal drugs," the promotion stated in a release. "Silva has admitted to taking the banned substance and agreed to participate in an approved drug-rehabilitation program and serve the six-month suspension."
The suspension dates retroactively to Nov. 10. Silva must pass a drug test prior to fighting again.
The Brazilian was suspended for one year following a win over Brandon Vera in January 2011 for submitting a fake urine sample to the Nevada State Athletic Commission. The win was later changed to a no-contest.