Excellent Question! There are many factors to this questions but to keep things short is yes I do believe marijuana can lower testosterone. Reports show THC lowers testosterone production in rodents, canines and primates, but for only 1 hour. However human studies on the same subject varied greatly on weather they were a chronic marijuana smoker or casual. casual smokers experienced almost no loss in testosterone.

You must also pay attention to the athletes diet if they are a smoker. Fitness enthusiast tend to stay away from cholesterol because of all the bad press it has got over the decades. However cholesterol is a pre-cursor for testosterone production. Staying active and lifting also keeps your testoerone leveled.

Alot of people feel lazy and unmotivated to work out after they smoke, to them I suggest waiting on the weed until after the work out. Marijuana is a wonderful anti-inflammatory and I believe this might be the best ways to see marijuana benefits as an athlete.

I like to have fun though and I dont think it affects me or my work out. I train BJJ daily and lift.

I'm sure if you were to ask UFC Fighter Nick Diaz if weed effects him negatively he'll probably laugh. Everyone is different and has different tolerances.