The Supreme Court ruled Monday that federal law supersedes state law on the medical use of marijuana and that federal authorities can prosecute patients even in the 11 states, including Maine, that have passed medicinal marijuana statutes. As difficult as it is for a sick person who might need marijuana to hear, the decision was correct.

Voting 6-3, the Supreme Court ruled that Congress was within its authority to regulate drugs and reversed a 9th Circuit Court of Appeals opinion.

As a practical matter, it’s unlikely the ruling will change the way drug laws are enforced in Maine. Most drug interdiction is conducted by local and state authorities, who aren’t likely to target cancer and AIDS patients who use marijuana, prescribed by a doctor, to ease pain or nausea or to counter other symptoms of illness.

The ruling created an unusual split on the court, with strong states’ rights advocates split from other conservatives. Justices Sandra Day O’Connor, William Rehnquist and Clarence Thomas voted against the ruling. In her dissent, O’Connor wrote that the “states’ core police powers have always included authority to define criminal law and to protect the health, safety, and welfare of their citizens.”

Maine voters passed the state’s medical marijuana law in November 1999. It authorizes adults to possess 2.5 ounces of marijuana or less, and have up to six plants, only three of which can be flowering, at any given time. Legal possession requires a prescription from a doctor. The law, however, is vague on how patients are supposed get the drugs, even with a prescription.

Efforts to rewrite drug laws in Congress to allow medical marijuana have failed, despite strong support among voters. That, however, is the best avenue for legitimizing the medicinal use of marijuana. As Justice John Paul Stevens, writing for the majority, said, Congress can always change the law: “But perhaps even more important than these legal avenues is the democratic process, in which the voices of voters … may one day be heard in the halls of Congress.”

In the end, federal law has supremacy over state law when the two conflict. It has to be that way. If the Supreme Court had ruled otherwise in this case – Gonzales v. Raich – it would have opened the gates for countless challenges of federal law by state governments eager to set their own rules. States would have essentially been allowed to establish their own drug policies, with implications far beyond medical marijuana.