In recent years, the public discourse on marijuana use in the United States has turned decidedly towards the side of liberty. Today, recreational use of the drug has been legalized in four states and decriminalized in fifteen, in direct opposition to federal law. With states taking policy into their own hands, it seems to be an opportune time to ask what, if any, are the Constitutional limits on the federal governments’ power to regulate marijuana.

Understanding these limits requires a correct understanding of the nature of the Constitution itself. As legal theorist Roger Pilon notes in his essay, ‘The Powers Delegated to the Federal Government Are Few and Defined: The Doctrine of Enumerated Powers’; “The doctrine of enumerated powers stands for the idea that Congress has only those powers that are enumerated in the Constitution, which the people delegated to Congress when they ratified the Constitution or later amended it.” The upshot of this interpretation is that, when asking if a regulation is constitutional, we should not look for rules prohibiting the regulation in question, but rather for specific authorization.

Since Federal marijuana laws are passed through Congress, the logical starting point is in Article I, which outlines most of Congress’ powers. Only one of the powers enumerated in this article could be construed to extend to marijuana: Article I, Section 8, Clause 3. This clause, typically referred to as the commerce clause, states that Congress shall have the power “To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes.”

What does this mean in practice? Madison and Hamilton make clear in Federalists 42 and 11 respectively, that the interstate commerce provision is only intended to grant power to regulate trade that crosses state boundaries, not trade that takes place within any given state. Thus it seems that marijuana regulation may be constitutionally justifiable, but only within strictly defined limits: regulation of sales and business across state lines. Even here, such regulations seem to fly in the face of the intent of the framers: Madison and Hamilton touted the commerce clause as a way to open up trade between states, not restrict it.

One thing is clear: this is certainly not enough authority to justify today’s sweeping federal bans. In fact, prohibition in the 1920’s had to be instigated through the 18th Amendment to the Constitution. This indicates an understanding that the Constitution as originally written did not authorize the federal government to prohibit disfavored substances as it does today.

To summarize, the Constitutional limits on the federal government’s regulation of marijuana are narrow: leaving only room for relatively modest policies. A correct understanding of the powers granted in the Constitution should prompt policy makers at the federal level to rethink their fundamental approach to the regulation of marijuana.