How do they know?

Check it out.  According the New York Times, scientists can tell whether testosterone in the body is synthetic (cheater) or natural (stud).  Scientist can measure the atomic weight of the of carbon atoms in the naturally occurring substance in the body then compare the atomic weight of the carbon atoms in the testosterone.  If the weights are the same, then dude is a study.  If they differ, dude is a cheat.

New York Times link

Get out your atomic scales and brush up on your periodic tables cuz we’re gonna boogie.