There are a number of different things that a number of countries have done. I'm most familiar with the United States. Actually, we in Canada are behind the game on this one in terms of a continental perspective.
In the United States...and I'm not sure if every state has limits, but I know that many states have limited the amount of certain products, specifically cold medications, that can be sold in a particular jurisdiction. They basically figure out what would be the legitimate consumption rate for a particular area, and then they only allow that amount to be distributed in that particular area. So there wouldn't be an opportunity for additional product to be sent out and then brought into the black market for the production of crystal meth. They also have legislation in many states that is very similar to what I'm proposing today.