The 9th Circuit's ruling held that the federal marijuana laws did not apply to medicinal use of marijuana in two specific cases. As you should know, the Constitution prohibits Congress from making laws on matters that lie outside its enumerated powers, which are very limited. One of those powers, though, known as the commerce clause, gives Congress the power to regulate interstate commerce. The commerce clause has become the conduit for Congressional abuse of the states and of the people.
Federal drug laws rely on the commerce clause for Constitutionality. Claiming that drugs are imported and sold throughout the United States, Congress applies its power to regulate interstate commerce to regulate, or ban, the possession and use of marijuana. The problem is, as the 9th found, growing, curing, rolling, and smoking pot does not require any commerce. It certainly doesn't require interstate commerce. Unless the government can prove that marijuana in one's possession came into his possession by way of another state, then the commerce clause cannot apply.
Many, including I, expect the Court to weasel its way out of this one. Conservatives tend to be more situational than principled. To anyone with a 3rd grade education, a backyard garden and interstate commerce are two different things, so Congress cannot regulate a garden. Regardless of one's view of marijuana, one's view of the government in Washington must be jaundiced with the understanding that, by stealing one piece of power from the people, Congress sets itself toward stealing all.
Watch this case closely, as it will foretell the future of freedom and government power for years to come.