Angel Raich and Diane Monson know plenty about the failings of modern medicine.
Ms. Raich has been diagnosed with an inoperable brain tumor, and Ms. Monson suffers from what her doctors say is a degenerative spine disease. Both women have tried virtually every form of medication legally available, but the multiple side effects from prescription drugs have only compounded their difficulties.
In searching for an alternative, and upon their physicians' advice, the two California residents started using marijuana. Both say it helps them cope with pain.
But, yes, there is a problem. While medical use of marijuana is authorized under a 1996 California law, federal law bans marijuana as an illegal drug.
Monday Raich and Monson's case arrives at the US Supreme Court where the justices must decide whether California law or federal law should apply.
How the justices decide the case could affect more than just the applicability of medical-marijuana laws in California and a handful of other states with similar provisions. It could redefine the balance of power between Congress and the states and become a signature decision of the Supreme Court under Chief Justice William Rehnquist.
"I think it will be a landmark, one way or the other," says Randy Barnett, a professor at Boston University School of Law, who is arguing the case for Raich and Monson.
Ultimately at issue in the case is to what extent the Constitution places limits, under the commerce clause, on Congress's ability to regulate areas that have traditionally been left to state and local jurisdictions.
Legal analysts say one aspect of the case that makes it particularly worth watching is the mix of a liberal policy issue - medical-marijuana use - with a constitutional principle embraced by conservatives - federalism (state sovereignty).
Will conservative justices support federalism even when it means upholding a liberal marijuana-use law that they would probably never otherwise endorse? And will liberal justices support the medical-marijuana provision even when their support of it might advance a view of federalism considered anathema by the court's dissenting liberal wing in earlier cases?
At the time the Constitution was written, the federal government's powers were sharply constrained to avoid conflicts with state and local laws. Other than a few areas subject to federal jurisdiction, all other areas were to be left to the states.
The Constitution specifically empowers Congress to regulate commerce among states. For much of the nation's history, this provision meant that Congress could pass laws concerning interstate trade and other activities among and between the states to facilitate the emergence of a national economy. But the controlling feature of the clause has always been how the high court defines "commerce."
In the late 1930s and early 1940s, the Supreme Court embraced a broad view of "commerce," ruling that congressional power to regulate the economy wasn't strictly confined to interstate commercial activities. The justices announced that congressional power could extend to intrastate activity, upholding federal regulation of wheat produced on a family farm - even when the wheat was grown for consumption only on the farm.
That landmark 1942 decision called Wickard v. Filburn opened the door for congressional regulation reaching down to the state and local level - as long as whatever was being regulated had an impact on "commerce," as it was broadly defined by the high court.
This definition permitted an explosive growth in national legislation that continued unabated until 1995, when the justices by a 5-to-4 vote struck down the Gun-Free School Zones Act. In 2000, the same 5-to-4 majority invalidated a portion of the Violence Against Women Act that authorized victims of gender-motivated violence to sue their attackers in federal court.
Many analysts say the medical- marijuana case places the high court at a crossroads. It can either continue the trend begun with its rulings in 1995 and 2000, or it can step back and authorize what some say would be even broader federal power at the expense of state sovereignty. "If the court upholds [the Justice Department's] claim of federal power, this case will supplant Wickard to become the most expansive interpretation of the commerce clause since the founding," say Robert Long Jr. and Professor Barnett in their brief to the court on behalf of Raich and Monson.
Acting Solicitor General Paul Clement says the medical use of marijuana cannot escape congressional regulation any more than farm-consumed wheat did in the Wickard case. If the federal government were unable to enforce federal drug laws within a particular state, it would undercut Congress's goal of effectively countering the illicit trade in narcotics.
"[Raich and Monson's] conduct is economic activity because it occurs in, and substantially affects, the marijuana market generally," Mr. Clement says in his brief.
Lawyers for Raich and Monson disagree. Monson grows her own marijuana at home. Raich, who is unable to grow her own, is supplied marijuana free of charge by two growers who use only supplies originating in or manufactured in California.
Some analysts are raising questions about the potential broad impact of a ruling in favor of Raich and Monson. They suggest that it could complicate enforcement of federal child-pornography laws and other statutes.
Barnett says such concerns are overblown: Cases involving possession of child pornography within one state could be turned over to state prosecutors.