I actually don't think it will take that long. Recreational use across the board could take some time, but even that might break sooner rather than later just because of the tax revenues involved and the fact that most law enforcement/prosecutors have come out on the common sense side of the equation and realized prohibition has never worked. I don't think all drugs will ever be legal across the board, and that probably shouldn't happen, but the MJ thing is just dumb, and I think more and more people are going to listen to reason.

There is a tipping point at which even some of the most skeptical folks on MJ will come to the conclusion the US policy here does not make sense on any level. If CO and some of the other states do this right, and to my knowledge there has not been very many problems with it so far, with it still polling well over 50% still in favor now that they have seen the program in action, you could see a swift change. This is shaping up to be just like alcohol. As more and more states legalize, national opinion will likely follow faster than you think.

As for the medical end of this, it should be a no brainer. If Canada is successful, that will also help tip the US polling in favor quickly. I don't think it is a matter of if, but when.