Morocco's Jamel Chatbiw withdrew from the world championship men's steeplechase final in berline today after testing positive for the stimulant clenbuterol.
An International Association of Athletics Federations spokesman says it's the first positive test from about 600 conducted so far.
Clenbuterol is often used to treat asthma.
Chatbi had finished second in heat three in the first round on Monday with the 11th best time overall.
He pulled out only hours before the event won by Kenya's Ezekiel Kemboi.