Yesterday WFAA, the ABC station in Dallas, reported that more than 100 people in Texas had been sickened by a bad batch of synthetic marijuana sold under the K2 brand. Today the Drug Enforcement Administration (DEA) rode to the rescue. Together with various other federal, state, and local law enforcement agencies, the DEA served about 200 search warrants and arrested more than 150 people in 29 states as part of "an ongoing effort targeting every level of the dangerous global synthetic designer drug market." Agents seized "hundreds of thousands of individually packaged, ready-to-sell synthetic drugs as well as hundreds of kilograms of raw synthetic products to make thousands more," along with "$20 million in cash and assets."

What's all the fuss about? The DEA explains that "smokable herbal blends marketed as being 'legal' and providing a marijuana-like high have become increasingly popular, particularly among teens and young adults, because they are easily available and they are more potent and dangerous than marijuana." According to the DEA, then, marijuana prohibition has driven people to "easily available" but more dangerous alternatives. The solution? More prohibition! In 2011 the DEA administratively added five chemicals used in pretend pot to Schedule I of the Controlled Substances Act. The Synthetic Drug Abuse Prevention Act of 2012 listed those substances and added 10 more synthetic cannabinoids. A DEA rule that took effect in February names four more.

But there are hundreds of other compounds, known and unknown, that can mimic the effects of THC, marijuana's main psychoactive ingredient. Just the products seized today (which included stimulants sold as "bath salts") contained "200 or 300 different identified chemicals," according to a DEA spokesman. The 2012 statute tried to address that problem by purporting to ban, in addition to 15 specific synthetic cannabinoids, a general class of "cannabimimetic agents," defined as cannabinoid receptor type 1 agonists in any of five structural classes. But if the DEA was confident of that approach, why did it bother to ban another four synthetic cannabinoids this year? And why doesn't the DEA's press release mention the 2012 law, which seems tailor-made for today's busts? Instead it reaches back to a 1986 law that is notoriously difficult to enforce:

While many of the designer drugs being marketed today that were seized as part of Project Synergy are not specifically prohibited in the Controlled Substances Act (CSA), the Controlled Substance Analogue Enforcement Act of 1986 (CSAEA) allows many of these drugs to be treated as controlled substances if they are proven to be chemically and/or pharmacologically similar to a Schedule I or Schedule II controlled substance. Synthetic drug cases prosecuted under this analogue provision have grown steadily in recent years as this problem has evolved. It has proven to be an effective tool to combat these new and emerging designer drugs.

If the 1986 law is adequate to "combat these new and emerging designer drugs," why did the DEA lobby for new legislation? Presumably because of the barriers to successfully prosecuting people under the analog drug law. For one thing, the substance has to be "intended for human consumption," which is why peddlers of ersatz cannabis deny any such intent, typically labeling their products as "incense." The chemical also has to be "substantially similar" to a Schedule I or II drug, and what that means is anybody's guess. Finally, it has to have a "stimulant, depressant, or hallucinogenic effect" similar to that of a Schedule I or II drug, or at least be represented as having such an effect. So if a guy hawks a product that contains a chemical structurally similar to THC by urging potential customers to "buy my simulated pot, which will get you high just like the real stuff," prosecuting him would be pretty straightforward. Otherwise it might be iffy. And even if a substance qualifies as an analog in one case, the exact same compound might not be deemed an analog in another case, since the definition can depend on context and subjective judgments of similarity.

The DEA spokesman tells me I should not read too much into the omission of the ban on "cannabimimetic agents" from the agency's discussion of prosecuting people for selling drugs that are not specifically prohibited by the CSA. Federal prosecutors will decide for themselves the best legal strategy, he says, and some of them may try their luck with the new provision. I called the Justice Department to find out whether there have been any successful prosecutions under that section of the 2012 law, but I have not heard back yet.

Prosecutorial strategies aside, does this seem like a good way to reduce the harm caused by drug use? As KFAA explains, "K2 is difficult to regulate because manufacturers switch up the ingredients frequently." And why do they do that? To stay ahead of the law. The upshot is that a relatively benign ingredient may be replaced on the sly with something less fun or more toxic. And as the DEA implicitly admits, legal restrictions on marijuana—a well-researched drug that humans have been consuming for thousands of years, a drug that the president of the United States correctly calls safer than alcohol—are encouraging people to experiment with novel chemicals that may prove far more dangerous.