CJ Ujah won the 100m at the 2021 British ChampionshipsBritish sprinter CJ Ujah has been suspended from competition after testing positive for a banned substance.
Ujah, 27, was part of Team GB men's 4x100m relay team which won silver at the Tokyo 2020 Olympics this month.
He has been provisionally suspended, the Athletics Integrity Unit (AIU) said.
The AIU said a test showed the "presence/use of a prohibited substance (Ostarine and S-23)."
A UK Athletics spokesperson said the governing body does not comment on ongoing processes.
Ujah, who has yet to comment, won the 100m at the British Championships in June.
Britain's men's quartet missed out on the 4x100m title by just a hundredth of a second in Tokyo.
Ujah ran the opening leg as anchor runner Nethaneel Mitchell-Blake was overhauled on the line by Italy's Filippo Tortu.
World Athletics Anti-Doping rules state that in instances where an athlete who has committed an ADRV competed as a member of a relay team, "the relay team shall be automatically disqualified from the event in question, with all resulting consequences for the relay team, including the forfeiture of all titles, awards, medals, points and prize and appearance money".
Enobosarm, or Ostarine, is listed as an anabolic agent - banned at all times - in the World Anti-Doping Agency's list of prohibited substances.
The UK Anti-Doping (Ukad) website said it has "similar effects to testosterone".
S23 is a Selective Androgen Receptor Modulator (Sarm), which, according to the United States Anti-Doping Agency (Usada) "have similar anabolic properties to anabolic steroids".
Ujah can request analysis of the B-sample - kept for storage while the A-sample is analysed - and should that confirm the Adverse Analytical Finding [AAF], the case will be referred to the Anti-Doping Division of the Court of Arbitration for Sport [Cas ADD].
In turn, the International Testing Agency (ITA) said: "The Cas ADD will consider the matter of the finding of an Anti-Doping Rule Violation [ADRV] and the disqualification of the men's 4 x 100 relay results of the British team".
Three other athletes have been suspended after tests carried out during the Tokyo Olympics.
They are Moroccan 1500m runner Sadik Mikhou, shot putter Benik Abramyan of Georgia and Kenyan sprinter Mark Otieno Odhiambo.
