Stephan Bonnar and Dave Herman both tested positive for banned substances at their UFC 153 drug test with Bonnar testing positive for a steroid and Herman testing positive for marijuana. 
UFC Executive Marc Ratner announced the drug test results today and MMAJunkie.com was the first news source to report the positive drug test.
Following the announcement of the positive drug test, the UFC released a statement via a press release.
“Stephan Bonnar and Dave Herman tested positive for banned substances following their bouts at UFC 153,” the statement said. “The UFC has a strict, consistent policy against the use of any illegal and/or performance-enhancing drugs, stimulants or masking agents. Both fighters have admitted taking the banned substances and have orally agreed to suspensions. Once the suspensions have been reduced to written agreements, the results of their tests and the agreed upon suspensions will be sent to the Association of Boxing Commissions official record-keeper so other jurisdictions will be on notice.”
With their not being an athletic commission in Brazil, the UFC handled the drug test and all 24 fighters that were on the card were tested.
Bonnar tested positive for the steroid Drostanolone, which is an anabolic steroid. According to Wikipedia, this steroid is primary used by bodybuilders and is mainly used in “cutting cycles.”
This is the second time in his career that Bonnar has tested positive for a steroid. Back at UFC 62 in 2006, he tested positive for Boldemone and admitted after the positive test that he took the drug to help his recovery from an injury.
This is also the second time that Herman has tested positive for marijuana. Prior to UFC 136, he tested positive for marijuana in a pre-fight drug test and was pulled from the bout.
The UFC did not announce the length of the suspension, but it’s likely that Herman will be cut from the UFC after the lost at UFC 153 and his second positive drug test in the company.