

Human beings sometimes have a troubling inability to hold two thoughts in mind at the same time. This is true not only when the two thoughts contradict each other but even when they simply appear to be in conflict with each other but actually aren't. And nowhere is there a greater need for us to get past this tendency than when discussing the ongoing war on drugs and the growing movement for the decriminalization of marijuana. It should be possible to say both that:

1) The drug war is an all-out disaster that has inflicted an untold amount of unnecessary human suffering. Therefore, as a first step toward ending this failed war, we should continue with the movement toward the decriminalization of pot.

And that:

2) There is scientific evidence of the dangers of pot on the development of adolescent brains, and for users of any age who end up abusing the drug. So, as we decriminalize, we should take every step possible to minimize the harm.

Those two positions are not actually contradictory, but in the polarized, zero-sum world that passes for policy debate right now, many act as if they are.

For the last 15 years I have been writing and speaking about the imperative of ending the disastrous war on drugs. In fact, in 2000, when I organized shadow political conventions to spotlight the major issues that neither political party was seriously addressing, the failed war on drugs was one of the three issues that we chose (growing inequality and the need for campaign-finance reform being the other two).

So it is definitely cause for celebration that the drug war, at least when it comes to pot, is finally deescalating. And after years of slow progress, the issue is gathering momentum. On Sunday The New York Times, in the first installment of a six-part interactive editorial, called for an end to prohibition. "The federal government should repeal the ban on marijuana," the editorial states. "We reached that conclusion after a great deal of discussion among the members of The Times's Editorial Board, inspired by a rapidly growing movement among the states to reform marijuana laws."

It's about time, as the drug war has been one of the worst domestic-policy catastrophes in American history. The human toll has been staggering. Drug offenders make up fully half of our massive inmate population. Of those, nearly 28 percent are locked up for marijuana-related offenses. In 2012 some 658,000 people were arrested for marijuana possession, and fighting marijuana use alone costs federal and state governments $20 billion a year. And the targets of the war on drugs have disproportionately been people of color. African Americans, for instance, make up 14 percent of habitual drug users yet constitute 37 percent of those arrested on drug charges.

So while we fight to change our drug laws, let's do so with a full understanding of the science. The effects of marijuana are not easy to study; people don't use it in the clean ways it's studied in labs. But we do know that in addition to marijuana providing relief to people undergoing chemotherapy and those suffering from glaucoma, multiple sclerosis and AIDS, among other conditions, there is clear evidence of the harmful effects on adolescent brains and on those who become addicted to it.

So let us not make the mistake -- the same one that climate-change denialists have been making -- of ignoring the science that we are afraid will weaken our position. Indeed, as we move toward legalization, let's put the science front and center. One of the worst things about the drug war is the way its proponents ignore the facts in favor of dogma. Let's not make the same mistake as we move toward legalization.

While we can't be certain about what lies ahead, we can take what we know now -- from the science on marijuana, from the market forces already in play and from our past experience with how marketing and market forces played out with tobacco and alcohol -- and at least try to create a system that anticipates and minimizes the inevitable downsides.

Mark Kleiman, a professor of public policy at UCLA and a co-author (along with Jonathan Caulkins, Angela Hawken and Beau Kilmer) of Marijuana Legalization: What Everyone Needs to Know, is worried that in our haste to get out from under the ills of a horrible drug war, we're not really thinking about what comes next.

"At the moment," he told me, "we're stumbling toward a commercial system, which I think of as the second-worst option, with only continued prohibition having worse likely outcomes."

To begin to understand this point, let's look at some of the recent scientific findings, the most notable of which has centered on the effects of marijuana on young people. A study published in The Journal of Neuroscience in April, conducted by researchers from Massachusetts General Hospital/Harvard Medical School and Northwestern University's Feinberg School of Medicine, showed how smoking marijuana, even occasionally, physically changes the young user's brain structure. "The results of this study indicate that in young, recreational marijuana users, structural abnormalities in gray matter density, volume, and shape of the nucleus accumbens and amygdala can be observed," write the authors.

Dr. Anne Blood, a professor of psychiatry at Harvard Medical School and one of the senior authors of the study, provided some context on the region of the brain where these abnormalities occurred. "These are core, fundamental structures of the brain," she said. "They form the basis for how you assess positive and negative features about things in the environment and make decisions about them."

Dr. Staci Gruber, a professor of psychiatry at Harvard Medical School who has also conducted studies on what marijuana does to the brain but was not involved in this particular study, had this advice for young people:

Don't do it early -- prior to age 16. That's what our data suggests, that regular use of marijuana prior to age 16 is associated with greater difficulty of tasks requiring judgment, planning and inhibitory function as well as changes in brain function and white matter microstructure relative to those who start later.

These findings are particularly worrisome because, as a 2013 study led by Gruber points out, "[m]arijuana use continues to rise, and as the perceived risk of [marijuana] approaches an all-time historic low, initiation of [marijuana] use is occurring at even younger ages."

There have also been at least two studies showing how marijuana use can impair working memory, one published in Schizophrenia Bulletin in 2013, and another in 2012. "Impairment of working memory is one of the most important deleterious effects of marijuana intoxication in humans, but its underlying mechanisms are presently unknown," wrote the authors of the latter study, published in the journalCell, which also noted that "long-term depression is associated with impairment of spatial working memory."

A 2014 study led by Dr. Rajiv Radhakrishnan of the Yale University School of Medicine concluded that while "it should be remembered that the majority of individuals who consume cannabis do not experience any kind of psychosis," acute exposure can "produce a full range of transient symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to some of the features of schizophrenia." Adolescent marijuana users, the study found, face an increased risk of developing such outcomes later in life. And for those suffering from existing psychotic disorders, marijuana use was found to "exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness."

There have also been studies showing direct links to depression. One from 2011 by researchers in the Netherlands found that for young people who are genetically predisposed to the condition, "smoking cannabis leads to an increased risk of developing depressive symptoms."

And a 2012 study published in the Proceedings of the National Academy of Sciences found that "the most persistent adolescent-onset cannabis users evidenced an average 8-point IQ decline from childhood to adulthood." The same effects were not found for users who began later in life. And more worrisome was that, for those who had started early, the negative effects continued even after they stopped using. "Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents," the study states. Or, as study researcher Madeline Meier, of the Duke Center for Child and Family Policy, told CBS, "Parents should understand that their adolescents are particularly vulnerable."

Co-author Dr. Richie Poulton, of the University of Otago in New Zealand, summed it up: "For some it's a legal issue, but for me it's a health issue."

As it should be for us all. Treating it as a legal issue has caused devastating harm. But ignoring marijuana's health risks will lead to young people using pot without being fully informed and educated about the risks of lifelong damage.

But the public's understandable eagerness to end the drug war has outpaced awareness of potential problems to come. According to a Pew Research Center poll from last year, while for the first time a majority of all Americans want marijuana legalized, for millennials the number is 65 percent. And the National Institute on Drug Abuse reports that 60 percent of high-school seniors don't see the harm in routine marijuana use, and over a third said they'd smoked it in the prior 12 months. In 1993 only 2.4 percent of high-school seniors said they used marijuana daily; by 2013 the number was up to 6.5 percent. And over 12 percent of eighth graders said they'd tried it. As use has gone up, so has the concentration of THC found in most marijuana. "Daily use today can have stronger effects on a developing teen brain than it did 10 or 20 years ago," said Dr. Nora Volkow, director of the National Institute on Drug Abuse. And in recent years 97 percent of new marijuana users have been 24 years old or younger. Clearly, young people are going to be the primary market for a legal pot industry.

Most of them won't abuse the drug when it's decriminalized, but some will. How many? Well, there's been research on this too. Kleiman and his co-authors write that, right now, about 4.4 million people meet the clinical definitions for either marijuana dependence or marijuana abuse. They also report on the work of epidemiologist James Anthony, who estimates the "capture rate" (the rate of people ending up dependent on a drug after trying it) for marijuana to be around 9 percent, compared with 15 percent for alcohol and 16 percent for cocaine. But when Anthony and his colleagues looked at those who began using marijuana before turning 25, the rate jumped to 15 percent. And an Australian longitudinal study with nearly 2,000 participants found that 20 percent of those who began using marijuana in their teens showed signs of dependence at 24.

And the fact that from 2013 to 2014 -- after marijuana was decriminalized in Colorado -- applications to the University of Colorado-Boulder increased by 33 percent, compared with a 2-percent increase the previous year, suggests that legal weed can have a magnetic pull on young people (even if some of the increase is due, as administrators claim, to the adoption of the Common Application).

Marijuana, according to Kleiman, was involved in 350,000 drug-treatment admissions in 2009, a number that has quintupled since 1992. And the majority of those were teenagers and young adults, with those below 21 accounting for nearly half of the admissions.

So the big challenge, as we go forward into a commercial marijuana market, is how to protect the most vulnerable: adolescents, young people and those of any age who are likely to end up abusing marijuana. And that's the problem with the current, laissez-faire way in which decriminalization is happening: There's a perverse incentive by those marketing marijuana -- already a multibillion-dollar industry -- to get people hooked. As Marijuana Legalization puts it:

The more-than-weekly users account for more than 90 percent of marijuana demand. That has a frightening implication: if we create a licit industry to grow and sell marijuana, the resulting businesses will have a strong profit incentive to create and sustain frequent and abusive consumption patterns, because the heaviest users consume so much of the product. So if we create a licit market, we should expect the industry's product design, pricing, and marketing to be devoted to creating as much addiction as possible.

This could lead, as Kleiman put it, to "a cannabis industry whose commercial interest is precisely opposite to the public interest" the way, over decades, we have had a tobacco industry and an alcohol industry whose commercial interests have been precisely opposite to the public interest.

Kleiman continues:

So from the perspective of cannabis vendors, drug abuse isn't the problem; it's the target demographic. Since we can expect the legal cannabis industry to be financially dependent on dependent consumers, we can also expect that the industry's marketing practices and lobbying agenda will be dedicated to creating and sustaining problem drug use patterns. The trick to legalizing marijuana, then, is to keep at bay the logic of the market -- its tendency to create and exploit people with substance abuse disorders. So far, the state-by-state, initiative-driven process doesn't seem up to that challenge.

So getting rid of horrible drug laws (a good thing) doesn't mean we shouldn't replace them with rules and regulations to minimize a new and different set of harms. The key is to do it now and not wait for a few decades -- and a lot of suffering -- to pass before we fix problems that could have been avoided. For example, take the story of the tobacco industry. In 1960 the Federal Hazardous Substances Labeling Act was enacted, allowing the FDA to regulate hazardous substances, but tobacco wasn't considered a hazardous substance at the time. So it wasn't until the Federal Cigarette Labeling and Advertising Act of 1965 that warning labels were required. And it wasn't until 1971 that broadcast advertising for tobacco was prohibited. Now there are regulations of all kinds aimed at limiting the tobacco industry's ability to target young people. For instance, tobacco companies can't, with their brand name, sponsor musical or sporting events, nor can they sell T-shirts and hats with cigarette brands on them.

But at least in the case of tobacco, the delay in setting up a framework to minimize harm was partially because it took a while for the science to come in. With marijuana the science is here. It's complex, and there will always be skeptics (as there still are in climate science and even tobacco, until recently) challenging the results, but we need to start including, in both our policy discussions and our reporting, the scientific findings we already have, especially because there are ways to limit the potential downside, including keeping the price of pot high, undercutting the political leverage of the burgeoning marijuana industry, protecting young people from marketing techniques we know they're susceptible to and educating the public about not just the medical benefits of marijuana but the possible negative consequences.

After many years of a horribly destructive and wasteful war on drugs, we are finally poised to bring an end to this shameful chapter in our country's history. But, as we look ahead to the next chapter, it's our collective responsibility to keep the science at the forefront of how we roll out legalization. We can learn a lot from the long history of trying to mitigate the harm of tobacco and alcohol. We don't need to make the same painful mistakes again.

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