Efimova had been provisionally suspended by swimming governing body Fina in March after a positive test for meldonium, the endurance-boosting drug banned as of January.

She was facing a lifetime ban as a two-time offender after serving a 16-month suspension after testing positive for the steroid DHEA in late 2013.

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In May Fina, however, lifted her suspension after the World Anti-Doping Agency said athletes testing positive for meldonium early this year could have taken it before it was banned.

But when Fina issued a list of seven Russian swimmers banned in the wake of the damning McLaren Report on state-backed doping in Russia, Efimova’s name was on it.

Efimova, like others, took her case to the Court of Arbitration for Sport, which wrestled with a welter of appeals right up until Friday’s opening ceremony in the confusion that followed the International Olympic Committee’s refusal to issue a blanket ban of Russia.

Russian swimmers Vladimir Morozov and Nikita Lobintsev, both banned after their names came up in the independent probe that found Russian officials manipulated drug test samples, were reinstated on Thursday.