Sprinter Asafa Powell's career is in doubt after his tests on his B sample showed an "adverse analytical finding".
The former world record holder was one of five athletes who tested positive for performance-enhancing substance oxilofrine after the Jamaican national trials.
A statement from the Jamaica Anti-Doping Commission "confirmed the prohibited substances which were identified in the A sample analyses for the five athletes who were tested at the National Junior and Senior Championships in June 2013".
American sprinter Tyson Gay, who holds the fastest time in the world this year over 100m, admitted to testing positive for a banned substance.
