Do me a favor...
Go into to Google and see if you can find the chart that shows how prescription painkillers (mainly opioids) were sought at a MUCH lower rate once medical mj was available.
Ask yourself why, though I think there is enough evidence out there about how applicable it is as a painkiller.
Now, go check with ANYone you know that plays college football or played it. Most of them had to deal with regular pain, playing in pain, and overcoming pain.
In fact, "Playing through pain" is often one of the attributes that people admire most in a player (remember Byron Leftwich playing with a broken leg and being carried by his linemen?)
We expect athletes to play through pain. But they have to live with that pain the rest of the days of the week. Some of those hits that we all love watching videos of (myself included in that group that loves watching them) end up affecting players for far longer than that one game.
So....
It shouldn't shock you AT ALL that players look for ways to deal with pain management, especially considering how addictive the other options are. Factor in potential brain damage from repeated concussions and you start making bad decisions anyway - since your reasoning is near the first thing affected.
Frankly, I am very confused by the league stance on a drug shown to treat pain effectively given the professional subjects its players to pain as a regular byproduct of play.