My friend G was one of the biggest guys in our school and yet displayed much speed and agility on the playing fields. His talents didn't go unnoticed and he was given a football scholarship to an American university. I went off to University in Toronto and enrolled in classes in philosophy, psychology and linguistics while he went south to play football and enrolled in classes in bowling and archery.
When I saw him again over the Christmas holidays that year I couldn't believe how much he had changed. He looked like he had packed on about 50 pounds of muscle. He wasn't shy or secretive about it, he told me that the team medical staff had put him on a course of anabolic steroids. This was just what every school did and every professional football player as far as he knew also injected himself with the stuff.
Ricky Williams has been twice suspended from NFL football for testing positive for marijuana use. This is somewhat bizarre since nobody is claiming that it has given him any advantage while working as a professional running back (unless it's actually what suppresses his fear while running full speed into 350 pound linemen). Meanwhile it is pretty likely that almost all of the larger players in the NFL and Major League Baseball have used or still continue to use performance enhancing drugs.
Unlike alcohol or anabolic steroids; marijuana is not known to make the user violent or aggressive. So it's use is quite irrelevant for a football player. It also does not make one particularly quick, either mentally or physically. This is why the Olympic people rightly reversed Ross Rebagliati's initial disqualification of his gold medal win in the snowboarding event after he tested positive for THC.
The video below could be made into a very useful public service announcement.