In the middle of 2020, the World Anti-Doping Agency’s investigative unit sent the agency’s top officials a report containing a stark warning based on an interview it had conducted with a doctor who had worked in China’s sports ministry.

The doctor claimed that China had been running a state-backed doping program for decades, a potential nightmare scenario for the Olympic movement, which was still recovering from a Russian doping scandal that had rocked the Games.

And while the doctor’s information was years old — she had defected in 2017 — it was specific. Among the ways Chinese athletes were cheating, she said, was by taking undetectable amounts of a little-known prescription heart medication, trimetazidine, or TMZ, which can help increase stamina, endurance and recovery.