British sprinter CJ Ujah's 'B' sample has tested positive, confirming the result of his initial test from the Tokyo Olympics.
Ujah, 27, was part of the British men's 4x100m relay team which won silver at the rearranged 2020 Olympics.
They will now almost certainly lose those medals.
Ujah was provisionally suspended when a test taken at the Games - his 'A' sample - tested positive for banned substances Ostarine and S-23.
Athletes have the right to request that a back-up sample, taken at the same time as the A-sample, be tested to confirm the initial result.
Ostarine is listed as an anabolic agent - banned at all times - in the World Anti-Doping Agency's (Wada) 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) has "similar anabolic properties to anabolic steroids".
The International Testing Agency said the case has now been referred to the Court of Arbitration for Sport Anti-Doping Division, which will rule on whether the British relay team - also including Zharnel Hughes, Richard Kilty and Nethaneel Mitchell-Blake - should be disqualified.
Olympic and World Athletics' rules state "where the athlete who has committed an Anti-Doping Rule Violation competed as a member of a relay team, the relay team shall be automatically disqualified from the event in question... including the forfeiture of all titles, awards, medals, points and prize and appearance money".