Editor’s note: While marijuana is forbidden by national and local laws, many of those laws are currently being challenged. For example, 16 states and Washington, D.C., now permit medical use of marijuana. Several states have ballot initiatives that would legalize production and non-medical use of marijuana. Mark Kleiman of the University of California at Los Angeles, Jonathan Caulkins of Carnegie Mellon, Angela Hawken of Pepperdine, and Beau Kilmer of Rand are the authors of a new book, “Marijuana Legalization: What Everyone Needs to Know,” a data-driven analysis of the potential costs and benefits of legalizing marijuana use. THE AMERICAN Editor-in-Chief Nick Schulz recently asked the authors about the implications of lowering the criminal sanctions designed to discourage pot use.

Nick Schulz: What’s the difference between “legalization” of marijuana and “decriminalization”? Why does this distinction matter?

Mark Kleiman et al: “Decriminalization” typically refers to eliminating criminal sanctions for users — effectively meaning those possessing amounts suitable for personal consumption (typically an ounce or less). Most of the research on decriminalization suggests the effect on consumption is small. "Legalization" usually refers to allowing commercial production and sale. Depending on the details of prices and regulations, the effect on consumption (including the part of consumption that involves drug abuse rather than simple harmless pleasure) might be very large.

NS: One argument against decriminalization/legalization is that the marijuana of today is far more potent than a generation or two ago. Is this true and is this relevant for the debate?

MK: It is more potent. And greater potency (and perhaps also a higher ratio of the intoxicating THC to the calming CBD) probably means greater risk to users. So does the lower age-at-first-use. Pot initiation was primarily concentrated among young adults in 1968; within a decade, it had shifted to the high-school age. By now there's a substantial amount of use in middle school. Younger brains are, we think, more vulnerable.

There are more than 750,000 arrests for marijuana possession each year — that's one of the most common reasons for arrest nationwide.

But both of those unfavorable trends have taken place under prohibition. It's not clear that any legal change could reverse the age trend, but it might be possible to put potency restrictions on legal marijuana, and that might change the balance of the marketplace in the direction of reduced potency and better balance between THC and CBD. Of course, there's no guarantee that would result. Indeed, one could also argue that if taxes are based on the weight of the marijuana and not its THC content, this could push the market toward greater potency. Thus, the net effect on potency will depend on the regulatory regime and level of enforcement.

NS: What do we know about the so-called gateway effect — the idea that marijuana use leads to experimentation with harder drugs?

MK: Not much, at a causal level. There's clearly a correlation: People who use marijuana are more likely to use other drugs than people who don't, and those who start younger are more likely to use and become dependent on other drugs than those who wait. (The same is true of tobacco and alcohol, which are "gateways" to marijuana.) But whether changing marijuana availability would change the use of other drugs — and in which direction — remains unknown and probably unknowable.

NS: What do we know about the number of people incarcerated on marijuana offenses? What’s the sensible way to think about the debate over this subject?

MK: It appears that, at any one time, about 20,000 to 40,000 people are in prison in the United States on marijuana charges who otherwise would be on the street. The vast bulk of these people are growers and dealers, not simple users. Some additional number committed other crimes but go to jail or prison for violating probation or parole conditions by using pot. That's a lot of people, but it's not a large share of total incarceration (2.3 million) or even drug incarceration (500,000).

Information we gather while marijuana remains illegal can't tell us much about how the world would work if it were legal.

On the other hand, there are more than 750,000 arrests for marijuana possession each year — that's one of the most common reasons for arrest nationwide (more than for murder, rape, robbery, and burglary combined, though much less than for drunk driving). An arrest can mean a night in jail, and a night spent in jail can be much riskier than smoking pot. An arrest also means having a criminal history, and for some people may be the start of a long-term involvement with the criminal justice system. Reducing the number of marijuana arrests ought to be possible without legalization — we didn't have nearly as many such arrests even 10 or 15 years ago — but one benefit of legalization would be to reduce the number of such arrests.

Yet legalization would not eliminate marijuana-related arrests. Most proposals would still keep marijuana illegal for those under 21, and we know in California that those under 21 accounted for more than 40 percent of all marijuana arrests in 2010. There would also continue to be arrests for driving under the influence of marijuana, selling to minors, and possibly for consuming in public (depending on the local ordinance).

NS: Supporters of liberalizing marijuana laws point out that the health effects of alcohol use are considerably worse. What do you make of that argument? 

MK: As a statement of fact, it's true. Not quite so clear what that fact proves. There are two versions of this argument, and it's important not to confuse them.

There's a moral argument that might be phrased as "Some people like to drink; other people prefer smoking pot. We don't punish the drinkers unless their drinking makes them do something bad to other people. Smoking pot is, on average, less harmful both to smokers and to the people around them than drinking. Therefore, it's wrong to punish the less harmful activity when we don't punish the more harmful activity." That's a reasonable argument, and all its premises are true; how much weight it deserves you'll have to judge for yourself. Maybe we should tighten up on alcohol, given how much damage it does.

There's also a practical argument that might be phrased as "We should legalize marijuana in order to get people who are now drinking heavily to smoke pot instead, thus reducing the harm to themselves and others." That's a very powerful argument if you accept its premise; if legalizing marijuana reduced heavy drinking, even moderately, that benefit would swamp any possible costs of increased marijuana abuse.

But the premise might or might not be true. We know that pot-smokers, on average, use more alcohol than pot-abstainers. It's possible that legalizing marijuana would increase heavy drinking rather than reducing it. And such an increase could easily swamp any benefits from reduced marijuana arrests.

Information we gather while marijuana remains illegal can't tell us much about how the world would work if it were legal, so the only way to find out whether the substitution argument is true would be to legalize marijuana. Even then, you'd have to wait a couple of decades for things to find a new equilibrium.

So the moral argument is valid as far as it goes; for some people, it's dispositive. The practical argument would be powerful if it were true, but we don't know whether it's true.

NS: Public attitudes about marijuana legalization have shifted dramatically in recent years, with more people favoring liberalization of marijuana laws. What is driving these changes in public attitudes?

MK: Hard to tell. Familiarity must be part of the story; those who came of age before pot was common remain far more hostile to it than the Boomer generation and its successors. But the change in attitudes has taken place all up and down the age distribution. The continued high prevalence of marijuana use in the face of more than a generation of enforcement effort may have convinced some people that prohibition can't be made to work.

It's also hard to tell whether the current trend will continue, or whether a new approach to prevention will prevail. It wouldn't be the first time a public opinion trend about marijuana had reversed.

Nick Schulz is the editor of THE AMERICAN.

FURTHER READING: Schulz also writes “Is the Nation of Immigrants Becoming a Nation of Emigrants?,” “Mobility Matters: Understanding the New Geography of Jobs,” “Here’s How to Replace the Income Tax,” and “Hard Unemployment Truths about 'Soft' Skills.” Sally Satel says “This Is Your Brain on Drugs.” Scott Gottlieb discusses “The DEA's War on Pharmacies — and Pain Patients.”

Image by Dianna Ingram / Bergman Group