In the United States, possession and distribution of marijuana is nominally illegal. But you don't have to be Tommy Chong to know that pot's legal status is cloudy and confused. Growing and using "medical" marijuana is legal in 11 states, and in cities like San Francisco it's easy enough to find locally grown product. In addition to being inconsistent, as critics have long pointed out, the federal ban is also irrational. It treats marijuana differently than similar products for no obvious reason. People use prescription drugs, pot, and alcohol for the same purposes: to get high, relax, and dull pain. The consequences of abuse are similar: crashed cars, disease, and lots of wasted time. So, what makes marijuana special?

The irrationality of U.S. marijuana policy is not news. Support of legalization has made bedfellows of people like Willie Nelson and William F. Buckley Jr., backed up by Richard Posner and Dr. Dre. And a Supreme Court decision on whether the federal laws can trump state statutes in this area is expected any day. But the strange status of marijuana may also bring down the scrutiny of a different entity altogether: the World Trade Organization and its powerful condemnation of inconsistent national laws. The American ban on marijuana is what the WTO calls "a barrier to trade," raising the question: Can U.S. marijuana policy survive the tough scrutiny of world trade law?

WTO scrutiny of American drug laws may sound far-fetched, but then until recently so did WTO scrutiny of U.S. gambling or tax laws. U.S. gambling laws, like drug laws, are erratic: Online casinos are strictly prosecuted, but state lotteries and Las Vegas are tolerated. Citing such inconsistency, last November the WTO declared American gambling enforcement an "illegal barrier to trade in services." The fate of these gambling laws may be a guide to the future of American marijuana laws.

Do such WTO decisions have any teeth? Yes, because unlike other international bodies the WTO understands punishment. In his tenure as U.S. president, George W. Bush has obeyed exactly one international court decision: a WTO ruling that shot down his protections for American steel. The reason even Bush listens to the WTO is that the organization knows the one thing politicians fear: angry industries, especially farmers. The WTO has the power to authorize punitive economic sanctions, and those inevitably target politically sensitive exporters—like Florida orange growers or Midwestern wheat. And to such threats even the United States responds. Just as the mob gets what it wants by threatening your family, the WTO targets farmers, and for politicians that's even scarier.

Two WTO principles spell trouble for U.S. drug laws. The WTO demands that countries treat foreign products the same as domestic ones (the "National Treatment" principle); and it demands that when chemicals or drugs are banned, those bans be based on good science (the "Beef Hormone" principle). Both these requirements may present a problem for the United States in the pot wars, because neither science nor logic has ever played much of a role in American crackdowns on "reefer madness."

Consider "national treatment." The basic idea is that the United States cannot tax Canadian rye whisky at $10 a bottle without doing the same to Kentucky bourbon. Under  WTO law, taxing one but not the other is illegal discrimination. The analogy to marijuana is clear: Local marijuana-growing enjoys quasi-legal status in the United States, but the import of foreign marijuana is strictly banned. In trade terms, that's called illegal discrimination in favor of local producers. Does it matter that the medical-marijuana laws are the rogue efforts of a handful of states like California and Montana? No, said the WTO in its online casino case—while state laws may give rise to this inconsistency, federal systems are fully accountable for state action.

U.S. states, moreover, are protecting a valuable industry. Estimates are unreliable, but the organization NORML in 1998 estimated the domestic weed industry at $15 billion, making it the nation's fourth largest: larger than the tobacco and cotton, but smaller than soybeans and corn. When local laws happen to protect a valuable local industry against imports, the WTO becomes suspicious.

"Beware the Killer Drug 'Marihuana'—a powerful narcotic in which lurks: Murder! Insanity! Death!" This warning, from a 1930s U.S. government poster, raises a central U.S. defense to WTO charges: Doesn't the United States have the right to protect its citizens against harmful drugs? Yes, countries do have explicit permission to enact health-protecting trade-restrictive measures (in trade lingo, "sanitary and phytosanitary measures"). But import bans must also be supported by scientific risk analysis. And merely saying "Murder! Insanity! Death!" is usually insufficient.

That's what the Europeans found out when their ban on hormone-fed beef was struck down by the WTO in 1998. Europeans have long been suspicious of American cattle fed growth hormones, believing that eating hormone-laden beef leads to premature sexual development. But the WTO struck Europe's beef-hormone ban for want of good science. In WTO language, Europe failed to supply a "risk assessment that reasonably supports or warrants the import prohibition."

There's a difference: Unlike with hormone beef, no one denies that marijuana is harmful when abused. As with tobacco or alcohol, the United States clearly has the right to enact some controls. The problem may be justifying the distinct U.S. treatment of marijuana's health risks. The WTO rules can be read to demand that products of similar risks be treated similarly, and a cannabis pill may be a market substitute for prescription drugs, alcohol, and tobacco. All are harmful: Prozac makes people suicidal, alcohol destroys livers, and cigarettes* are cancerous and as addictive as crack. What, the WTO may ask, makes marijuana so different?

The issue is sharpened by the problem of the import of cannabis for medical purposes. The White House now denies that cannabis is a medicine, saying "even if smoking marijuana makes people 'feel better,' that is not enough to call it a medicine." But a 1999 medical study commissioned by the (Clinton) White House concluded otherwise, saying "the accumulated data suggest a variety of indications, particularly for pain relief, antiemesis, and appetite stimulation." Such findings cannot help the U.S. case.

The United States does have a fallback defense: Marijuana makes good people bad. The World Trade Organization allows countries to enact measures "necessary to protect public morals." Which raises this fundamental question: Is it wrong to be stoned? A 1924 Daily Mirror editorial said, "Marijuana inflames the erotic impulses and leads to revolting sex crimes." And today, according to the White House, "Marijuana users in their later teen years are more likely to have an increased risk of delinquency and more sexual partners." But just because smokers drop out and have more sex, is that sufficient to sustain a morality-based barrier on trade? No one knows, but it is the kind of question that makes trade law interesting.

In order for the WTO to consider the legality of U.S. drug laws, some country would have to bring a WTO complaint against the United States. Don't expect a case tomorrow, but it may just be a matter of time. An increasing number of countries—including Belgium, Holland, and Canada—have begun to allow licensed growing of marijuana, and today's growers will be tomorrow's exporters.

Canada is the natural WTO plaintiff. Just as with alcohol during prohibition, Canada makes lots of money selling contraband dope to its southern neighbor. According to the Canada's National Post, Canadian marijuana is a $7 billion industry, or larger than Canada's wheat and dairy industries, and its fisheries. And the laws up north are loose. The last two prime ministers have been legalization advocates. (Former Prime Minister Jean Chretien famously said, "The decriminalization of marijuana is making normal what is the practice. ... I will have my money for my fine and a joint in the other hand.") And some Canadian courts have even struck down marijuana laws as violative of fundamental rights. Even Tommy Chong (of Cheech and Chong) is from Alberta—the Canadian complaint at the WTO could well begin, "Hey, man …"

The economic incentives to bring a WTO complaint are clear. For Canadian and other marijuana exporters, the American recreational and medical weed market is the big fatty. Americans smoked 1,047 metric tons of ganja in 2000—according to U.S. government estimates, worth $10.5 billion. (The White House estimates that the average smoker goes through 18.7 joints per month.) Every afternoon, at 4:20, millions of bowls light across the nation—and what country wouldn't want a piece of that?

For many, these points may lead to questions not about the drug laws but about the WTO. But none of this should be a surprise. The WTO's reasoning is economic, and economic logic taken seriously often has radical consequences. Many economists, including Nobel-laureates Gary Becker and Milton Friedman, have long believed that American marijuana laws are irrational. And as William F. Buckley Jr. puts it, "marijuana prohibition has done far more harm to far more people than marijuana ever could."

The irony here is difficult to overstate. The same WTO that most stoners love to hate may someday be the organization that guarantees their supply. In the words of Willie Nelson, "Marijuana is an herb and a flower. God put it here. What gives the government the right to say that God is wrong?"

Correction, March 18: The article originally stated that nicotine was cancerous and as addictive as crack, but nicotine does not itself cause cancer—other substances in cigarettes do. (Return to the corrected sentence.)

Tim Wu is an associate professor at University of Virginia Law School. He teaches intellectual property and international trade.