Four UFC fighters have been suspended six months by USADA, all for testing positive for the banned substance ostarine, the UFC’s anti-doping partner announced Tuesday.

The four fighters were former UFC women’s flyweight champion Nicco Montaño, prospect Sean O’Malley, Augusto Mendes and Marvin Vettori. All had trace amounts of ostarine in their system in drug tests last year, which USADA says is consistent with supplement contamination. USADA found “no evidence of intentional use” in any of the four cases, per a release.

“The trace amounts of ostarine found in each of the athlete’s samples was made possible by sensitive laboratory detection capabilities,” USADA stated in a press release. “However, as detection windows increase and the potential time between ingestion and detection lengthens, it has become more difficult for athletes to identify a contaminated product that may be the source of their positive test. As a consequence, the investigation period in ostarine cases is frequently relatively long, as has been the case in each of the cases announced today.”

Of the four cases, O’Malley and Mendes were the only two that were publicly known. Mendes was announced by the UFC prior to a change in policy, while O’Malley announced the news of his positive drug test himself last September. Last summer, the UFC decided to change its policy on when positive drug test announcements were made, changing from as soon as the results got back to the completion of the investigation and adjudication process.

Montaño, 30, tested positive for ostarine in an out-of-competition sample collected Oct. 25, 2018. She was provisionally suspended Nov. 15, 2018 and her six-month suspension is retroactive to that date. Montaño is eligible to return to the UFC on May 15.

Montaño (4-2) has not fought since beating Roxanne Modafferi to win the inaugural UFC women’s flyweight title at the TUF 26 Finale in December 2017. The New Mexico native was supposed to defend the title against Valentina Shevchenko at UFC 228 last September, but withdrew after having to be taken to the hospital due to a bad weight cut. The UFC subsequently stripped Montaño of the title.

O’Malley, 24, failed a drug test stemming from out-of-competition samples collected Sept. 5, 2018 and Dec. 8, 2018. The two positive tests were treated as a single violation, because the amount in both samples was consistent with “ingestion prior to” the first positive. O’Malley’s ineligibility began Sept. 19, 2018, so he can return immediately. O’Malley was also suspended six months by the Nevada Athletic Commission (NAC) for the violation.

I’m freeeeee . July 6th I’m busting someone up . — Sean O'Malley (@SugaSeanMMA) April 23, 2019

Vettori, 25, came back positive for ostarine stemming from a sample collected Aug. 24, 2018. His period of ineligibility began on that date, so he can fight immediately. Mendes, 36, tested positive in a March 7, 2018 sample with an ineligibility period that started March 20, 2018. Mendes, a Brazilian jiu-jitsu standout, can fight in the UFC immediately, however he is no longer on the roster. “Tanquinho” asked for and was granted his release in June 2018.

Ostarine, which is in the selective androgen receptor modules (SARMs) family, has performance-enhancing properties and carries a suspension length of two years from USADA if intentional use is found. Ostarine is an illegal drug in the United States, though commonly found in dietary supplements as a contaminant.