As Massachusetts currently considers a more rational marijuana policy, some state legislators are using the flawed logic of prohibition to try to outlaw another plant they fear kids are using as a legal substitute for pot.

This past month, supporters of a ballot initiative that would liberalize this state’s marijuana laws through decriminalization were given a hearing at the Massachusetts legislature’s Joint Committee on the Judiciary. The proposed reforms, which voters might have a chance to consider in November, stem from the thinking that current criminal laws are a costly and ineffective way of actually keeping people from smoking pot or using other drugs. Making possession a civil rather than criminal offense would modernize the state’s drug policy, and would be more respectful of “the civil liberties of those having a harmless toke,” as the Phoenix wrote this past November, endorsing the proposal.

Even as this drug-liberalizing proposal is being debated, however, Republican state representatives Vinny deMacedo, of Plymouth, and Dan Webster, of Hanson, are opening another front in the drug war by seeking to list Salvia divinorum — a hallucinogenic plant that can be purchased legally online or in local smoke shops — as a Class C drug, along with LSD and marijuana. Seven states have already criminalized salvia, and North Dakota is currently prosecuting the first case under that state’s law.

But if preventing youths from using salvia is the goal, the history of drug prohibition suggests that criminalization may be the worst way to do it.

Salvia is a powerful entheogen — a “god-creating” substance that causes vivid spiritual feelings, altered perception, and hallucinations. Studies suggest, however, that salvia does not produce the euphoric high that, in other drugs, promotes addiction by triggering the brain’s “reward” circuitry. Indigenous groups in Oaxaca, Mexico — the plant’s native territory — have used it for years to achieve those spiritual states. But despite salvia’s non-addictive effects, deMacedo still labels it a “gateway drug.”

“Call me old fashioned,” he says, laughing, “but I think drugs are bad. When kids see a drug that is legal, there’s a feeling that it must be okay.” DeMacedo introduced House Bill 4434 on behalf of police in Plymouth and Hanover, who first heard from parents about MySpace posts and YouTube videos showing high-school students acting goofy while supposedly on the drug. (As of April 22, a YouTube search for “salvia” resulted in 3740 hits, many of which appear to feature kids who have smoked the drug, who then either seemed trapped in slow-motion bewilderment or in fits of convulsive laughter.) The legislators are concerned that, in an unregulated market, kids can access salvia easily.

DeMacedo’s fix for that unregulated-market problem, however, is not to regulate salvia, but to outlaw it.

The legislators’ underlying concerns are legitimate. In principle, currently anyone can buy salvia from smoke shops around the state (or online). And because scientists are as yet unclear as to its long-term effects, precaution suggests we might want to keep salvia out of teenagers’ hands. (That said, while there is little science to detail the risks or benefits of salvia, preliminary studies suggest that derivatives of its active chemical could be useful for treating cancer, Alzheimer’s, or even AIDS. But if the history of marijuana research is a guide, criminalizing salvia will freeze research into potential therapeutic applications.)

DeMacedo says he has neither evidence of hospital visits nor any data demonstrating salvia’s harm — the logical link between the existence of a drug and the need to regulate it. Armed with just the concerns of local police and buoyed by anecdotal evidence from YouTube, the Massachusetts legislators will need to convince the public and fellow lawmakers that salvia prohibition would work. Like other anti-drug advocates around the country, deMacedo and Webster are applying the logic of marijuana prohibition to the salvia dilemma, despite the fact that the current marijuana policy is demonstrably ineffective at keeping kids from smoking pot.

This country’s experience with prohibition has proven only that outlawing drugs creates underground black markets — on the street, it doesn’t matter how old you are, as long as you have cash. Those black markets are also ground zero for much of the violence and social disorder people attribute to drugs.

By contrast, alcohol regulations are much more effective at actually keeping alcohol out of kids’ hands. Massachusetts imposes strict penalties on bars and liquor stores that sell to minors, which in turn serves as a powerful deterrent. One local high-school student even says that he can buy marijuana much more easily than alcohol due to strict ID-checking policies.

As such, the primary hoped-for benefit of criminalization — reduced usage — might not occur. And enforcing drug laws is costly: for comparison’s sake, note that arresting and prosecuting marijuana offenses costs Massachusetts about $130 million per year, according to a 2005 study by Harvard professor Jeffrey Miron. Though enforcing salvia laws would be far cheaper, it reminds us that law-enforcement budgets could instead be going to health care or education.