Twenty-three Chinese swimmers tested positive for a banned drug before the Tokyo Olympics in 2021 but were cleared to compete after the country’s anti-doping agency found the results were caused by contamination.

The swimmers all tested positive for heart medication trimetazidine (TMZ) at a training camp seven months before the delayed Games.

China Anti-Doping Agency (Chinada) determined they had unintentionally ingested the substance and would not face any punishment.

China’s 30-member swimming team won six medals at the Tokyo Olympics, including three golds.

Details of the case were revealed by the New York Times,, external who shared reporting with German broadcaster ARD.

United States Anti-Doping Agency (Usada) chief executive Travis Tygart said it was “crushing” to hear of the positive tests before an Olympic Games.

He said the World Anti-Doping Agency (Wada) and Chinada had “swept these positives under the carpet by failing to fairly and evenly follow the global rules that apply to everyone else in the world”, while athletes “impacted by this potential cover-up” had been “deeply and painfully betrayed by the system”.

“All of those with dirty hands in burying positive tests and suppressing the voices of courageous whistleblowers must be held accountable to the fullest extent of the rules and law,” Tygart added.

Britain’s Olympic swimming champion Adam Peaty questioned why the information was not released earlier, adding: “So disappointing from Wada.”

Wada confirmed to BBC Sport it was notified of Chinada’s decision in June 2021.

The world body said it “carefully reviewed” the case and consulted independent experts to “test the contamination theory” as well as external legal counsel.

Wada concluded it was “not in a position to disprove the possibility that contamination was the source of TMZ”, the athletes bore “no fault” and an appeal against Chinada’s decision was “not warranted”.

Olivier Rabin, Wada’s senior director of science and medicine, added: “The contamination scenario was further supported by the combination of the consistently low concentrations of TMZ as well as no doping pattern with several athletes presenting multiple samples collected over the course of several days which fluctuated between negative and positive [and vice versa].”

Russian figure skater Kamila Valieva was ultimately given a four-year ban for doping after testing positive for TMZ in December 2021, shortly before competing in the 2022 Winter Olympics.

Chinese Olympic swimming champion Sun Yang served a three-month ban in 2014 after testing positive for TMZ. He is currently serving a separate doping ban, which was reduced from eight years to four years and three months in June 2021.

Swimming’s governing body World Aquatics, then known as Fina, was also notified about the adverse analytical findings (AAFs) in 2021.

World Aquatics said it was “carefully considered” by Fina’s doping control review board.

It added: “World Aquatics is confident that these AAFs were handled diligently and professionally, and in accordance with all applicable anti-doping regulations, including the World Anti-Doping Code.”

Chinada told the New York Times it found the swimmers had not broken anti-doping rules and was not obliged to publish details about the case without their consent.

Wada shared its conclusions with the International Testing Agency (ITA), which in 2022 raised issues regarding TMZ samples possibly being misreported.

Usada contacted Wada in April 2023 saying it had received a tip that positive TMZ cases had been hidden.

Wada said its intelligence and investigations department “concluded that proper procedures had been followed and that there was no evidence of wrongdoing”.

Gunter Younger, Wada’s director of intelligence and investigations, added: “The data held by us clearly showed that there had been no attempt to hide the positive tests as they had been reported in the usual way by the Chinese authorities.”

The ITA said it received “confidential and anonymous information” in summer 2021 about the positive tests.

It added: “In parallel to a full assessment of the information received that remains active, the ITA conducted many targeted follow-up testing missions in 2021, 2022, 2023 and up until today.”