A test for THG has only recently been possible, and lots of athletes have tested positive for it.
Old clean tests are also being looked at again to see if people were using THG before it could be tested for.
US athletics bosses have revealed that four unnamed athletes there have failed tests for THG.
They're determined to get rid of all the drug cheats from the sport, with anyone found cheating getting at least a two-year ban.
Chambers insists he didn't take the drug on purpose, and thinks it was in a supplement he was told was safe to use.
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What is THG?
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