Kenyan marathon star Peres Jepchirchir has been provisionally suspended after a sample collected before her victory at the Sydney Marathon returned an adverse analytical finding for erythropoietin (EPO), the Athletics Integrity Unit (AIU) has announced.

In a statement released on Friday, October 23, the AIU said the sample was collected out of competition in Kenya ahead of the 2026 Sydney Marathon, where Jepchirchir went on to claim victory.

EPO is a prohibited substance that stimulates red blood cell production, improving the blood’s ability to transport oxygen to muscles. Its use can enhance endurance performance and is banned under anti-doping regulations.

The provisional suspension prevents the reigning world marathon champion from competing as the case proceeds under the sport’s anti-doping rules.

The finding comes as a setback for the 33-year-old, who has established herself among the leading figures in international distance running.

Jepchirchir’s achievements include winning the London Marathon in 2024, the Boston Marathon in 2022 and the New York City Marathon in 2021, before adding the Sydney Marathon title in 2026.

She also won the women’s marathon at the Tokyo 2020 Olympic Games, held in 2021, and previously held the women’s half-marathon world record.

Her latest suspension follows a period in which she had been managing injury concerns. She withdrew from the 2025 London Marathon after suffering a stress fracture and later returned to competition at the Sydney Marathon.

The AIU’s announcement came a day after the agency imposed a six-year ban on Ethiopian distance runner Ruti Aga following a separate doping case involving methylprednisolone and interference with an investigation.

Jepchirchir’s case is now subject to the relevant anti-doping procedures. A provisional suspension following an adverse analytical finding is not, by itself, a final determination of an anti-doping rule violation.