Team GB risk losing their men's 4x100m Olympic silver medal from Tokyo 2020, after sprinter CJ Ujah tested positive for two banned substances.
The 27-year-old was found to have Ostarine and S-23 in his system following one of the relay races, drugs which are similar to anabolic steroids but according to the US Anti-Doping Agency, have "reduced androgenic (producing male characteristics) properties."
They are both Selective Androgen Receptor Modulators (SARMs), often used to build muscle, and UK Anti Doping (UKAD) says Ostarine is not approved for human consumption anywhere in the world.
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Ujah is provisionally suspended and now faces an investigation from The International Testing Agency (ITA), which is responsible for taking samples at the Olympic Games, before potentially facing sanctions, having been notified of the test result by the doping control laboratory in Tokyo.
He is one of four athletes being investigated, along with the previously announced trio of Bahrain 1500m runner Sadik Mikhou, Georgian shot put thrower Benik Abramyan and Kenyan sprinter Mark Otieno Odhiambo.
Disciplinary proceedings are underway against Ujah, and the Athletics Integrity Unit (AIU) says two of the four athletes were specifically targeted following a tip-off, although they have not been identified.
Ujah has not yet been proved guilty of any wrongdoing, and he is yet to make a comment, though it appears the result will come as a surprise after posting a tweet on Wednesday which simply said "back at it!" It is possible that he could request the results of B sample.

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He was on the first leg of the relay team which were pipped to gold by Italy in the final on Friday 13 August.
In a statement, the AIU said: “The AIU now awaits the conclusion of the ITA proceedings against the above athletes, which will determine whether any anti-doping rule violations have been committed and what consequences (if any) should be imposed in relation to the Olympic Games.
“Any consequences beyond the Olympic Games to be imposed upon the athletes under the World Athletics Anti-Doping Rules will be determined following the conclusion of the ITA proceedings.”
Ujah is the highest profile British track and field athlete to test positive for a banned substance since Dwain Chambers admitted to using performance enhancing drugs in 2003.
British Athletics and UKAD are yet to make a statement.
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