A medical marijuana case presently on appeal to the Supreme Court of these United States has the Bush Administration engaging in tortured, almost inconceivable legal logic. The government appealed from a circuit court ruling that held that entirely local, non-commercial marijuana use was beyond Congress' power to regulate interstate commerce. In its brief on the merits, the government argues that local use "substantially affects interstate commerce."
Meaning that local, non-commercial (and legal) distribution and/or use has an impact on the interstate (and illegal) distribution and/or use of marijuana. So, if you want to smoke your medical marijuana, you're just going to have to buy it on the street same as everybody else.
I'm almost tempted to file an amicus brief supporting the government on behalf of "unnamed independent pharmaceutical distributors."