Marathon star Peres Jepchirchir has been provisionally suspended from competition after a sample collected from her returned a finding of a banned substance, just weeks after she won the Sydney Marathon in August.

The substance identified is erythropoietin (EPO), a hormone that stimulates the production of red blood cells. Its synthetic form is banned in athletics because it can increase the amount of oxygen carried to muscles, helping endurance athletes maintain their pace over long distances.

In a statement on Friday, the Athletics Integrity Unit (AIU), which oversees anti-doping matters in athletics, said the sample was collected outside competition before the reigning World and former Olympic Champion travelled to Australia for the Sydney marathon.

“The AIU has provisionally suspended reigning World and former Olympic champion, Peres Jepchirchir, after an out-of-competition sample, collected in Kenya prior to her recent Sydney Marathon victory, returned an adverse analytical finding for EPO,” the organisation said.

The suspension is provisional, meaning the case has not reached a final determination. It temporarily bars Jepchirchir from competing while the anti-doping process proceeds, but does not by itself establish that she committed an anti-doping violation.

Jepchirchir, 32, won the Sydney Marathon on August 30 in 2:18:31, finishing more than three minutes ahead of compatriot Irine Cheptai, who clocked 2:22:11, and Ethiopia's Shure Demise finished third in 2:22:33.

The Kenyan missed the course record of 2:18:22, set by Dutch runner Sifan Hassan in 2025, by just nine seconds. The victory also made Sydney her fourth World Marathon Major title, adding to wins in New York in 2021, Boston in 2022 and London in 2024.

Jepchirchir rose to prominence as a half-marathon runner, winning the world title in 2016 and 2020 before moving on to the marathon. She won Olympic gold at the Tokyo Games in 2021, finishing in 2:27:20, and claimed the world marathon title in Tokyo four years later after beating Ethiopia's Tigst Assefa by two seconds.

She also set a world record of 1:05:34 in a women-only half-marathon in Prague in September 2020. A month later, she improved that time to 1:05:16 to win the world half-marathon title in Gdynia, Poland.

In December 2025, Jepchirchir set her marathon personal best of 2:14:43 in Valencia, Spain, finishing second behind compatriot Joyciline Jepkosgei, who won in 2:14:00.