The first question most fit people have about cannabis is, "How does it affect testosterone levels, body fat, and performance?" Well, the research is all over the damn place like spilled bong water:
Some people think weed lowers testosterone levels, which would obviously be bad for lifters and athletes. But the science, so far, is inconclusive.
Yes, you can find studies that show marijuana lowers testosterone, at least temporarily, among heavy daily users. BUT you can also find good studies that show it doesn't lower T levels at all.
And, get this, you can even find a couple of studies that conclude pot actually increases testosterone levels (again, at least temporarily).
Confusing, huh? And of course the pro-pot and anti-pot folks will just cherry-pick whatever studies support their views. So, it's a wash. We just don't know for sure how marijuana affects testosterone.
Well, science tells us that weed stimulates the appetite, lowers inhibitions, and makes food taste better. So, it kinda-sorta leads to fat gain, right?
Well, not really. Marijuana has also been shown to boost metabolic rate and improve carbohydrate metabolism. And statistically, regular users have the lowest rates of obesity, even if they happen to be visited by the Munchie Monster on occasion.
And honesty, the "munchies" thing is a bit overblown. "Drunk eating" is far worse and far more common.
Anecdotally, many top athletes and bodybuilders use cannabis, but that doesn't "prove" anything.
We can wade into the deep water and say that maybe they'd be even better without the weed... or we could say the stress and anxiety-reducing effects help them with recovery and sleep, which may trump any negative effects like impaired psychomotor abilities. As long as you don't compete stoned, that's probably not an issue anyway.
Also, many lifters say their best workouts are buzzed workouts. But others lose motivation if they toke it up and can't imagine training in that dopey state. That could be an indica vs. sativa thing too. Strains matter, kids.
So if you enjoy marijuana, your T levels are good, your body composition is fine, and you're building muscle, then go for it. Just be aware of the possible negatives.
Finally, marijuana can be a stress-buster. And stress and inflammation are pretty much at the root of most things that can shorten our lives. So if some of the negatives associated with cannabis turn out to be true, then you have to weigh them against its benefits, like stress reduction. Then, decide for yourself.