Botswana's Nijel Amos has been provisionally suspended ahead of next week's World Championships after the 2012 Olympics 800 metres silver medalist tested positive for a banned metabolite, the Athletics Integrity Unit (AIU) said on Tuesday.
Amos was notified of the result while in Eugene, Oregon, where he was scheduled to compete in the 800m heats on July 20.
The drug found in the 28-year-old's system, GW1516, "modifies how the body metabolizes fat," and the World Anti-Doping Agency has said it poses a health risk to athletes, AIU said in a release.
Amos could not be immediately reached for comment.
His silver from the London Games was Botswana's first Olympic medal. The African nation added a bronze in the 4x400m relay at the Tokyo Games last year.