A Swiss expert said on Thursday that the substance roxadustat that Simona Halep tested positive for is a problem for anti-doping agencies.

The substance Roxadustat and the complexity of the anti-doping fight in sports

Raphael Feis, chief scientist at the Center for Research and Expertise in Anti-Doping Sciences at the University of Lausanne, said the banned substance roxadustat was a problem for anti-doping authorities.

“(Roxadustat) is not new, it has been around since the early 2010s, but it was only available in Asia,” Feis told Reuters, as quoted by Agerpres.

“It stimulates the body as if it were at altitude and stimulates the rise of red blood cells, producing endogenous erythropoietin,” explained the Swiss expert.

Roxadustat, which has been detected in anti-doping tests since 2017, has a 10- to 16-hour elimination time, making it difficult for doping control officers to detect potential cheats.

Halep was provisionally suspended from October 2022 after her positive test at the US Open, with the Romanian vehemently denying she knowingly took the banned substance.

Simona Halep was heard by the International Tennis Integrity Agency (ITIA) in London this month and an announcement on the matter will be made shortly. Tennis fans were excited after Halep appeared on the preliminary list of players participating in the US Open.

Feis said athletes who train consistently at altitude for only a few days are suspect because they are difficult to test.

According to the World Anti-Doping Agency (AMA/WADA) location rules, athletes must report a 60-minute window each day they are available for testing. They must also provide the authorities with their personal address, places and periods of study.

“It is difficult to check athletes training at altitude, some places can only be reached by cable car, which does not operate at night,” Feis noted.