I'll give it a go:
marijuana has pain relieving/pain inhibiting properties. That's the whole "medical marijuana" scam that several states are using to allow marijuana sales. The argument that for many kinds of pain marijuana is a superior pain reliever, and in some cases the only functional pain reliever.
Can you think of any "performance enhancing" properties of taking a pain reliever that is significantly superior to any kind of over-the-counter pain reliever? Train harder, train longer, take more punishment than you could if you were not taking that pain reliever.
It isn't just banned because the fuzz is trying to harsh Nick's mellow.
There's much more effects than just pain relief, but I'll touch on this a bit.
Have you ever taken a pain reliever? Do you know the effects of "superior pain relievers"?
Let's list some:
According to the American Chronic Pain Association, common side effects include: constipation, nausea, vomiting, drowsiness, thought and memory impairment, and slowed reaction time.
Seems quite performance enhancing doesn't it? Especially for fighting. Now that's just for pain relievers.
Let's look at marijuana alone:
What are the effects of marijuana on performance?
Impairs skills requiring eye-hand coordination and a fast reaction time
Reduces motor coordination, tracking ability and perceptual accuracy
Impairs concentration, and time appears to move more slowly
Skill impairment may last up to 24 to 36 hours after usage
Reduces maximal exercise capacity resulting in increased fatiguability
Marijuana has no performance-enhancing potential.
http://espn.go.com/special/s/drugsandsports/mari.html
I think you fucking fail, kids.