NFL commissioner Roger Goodell was asked Friday during his Super Bowl press conference if the league, in light of marijuana legalization in Colorado and Washington, would be willing to change its stance on marijuana usage and abide by state laws.

"This has been something that has been asked several times and I'll try to be as clear as I possibly can: It is still an illegal substance on a national basis," Goodell said. "It's something that's part of our collective bargaining agreement with our players. It's questionable with respect to the positive impact but there is certainly some very strong evidence to the negative impacts, including addiction and other issues.