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Steve LEVITT: Carl Hart is not your typical academic. Trained as a neuroscientist and now a psychology professor at Columbia University, in his research studies, he brings heavy drug users into his lab for weeks at a time to observe how drugs affect them and to learn about their decision making. In his new book, Drug Use for Grownups, he argues for a radical overhaul of drug policy. He’s not just talking marijuana. In his ideal world, heroin, methamphetamines, cocaine — they’d all be legal. 

Welcome to People I (Mostly) Admire, with Steve Levitt.

LEVITT: I’ve been teaching undergraduates about drug policy for two decades, and I definitely haven’t been teaching them what Carl Hart advocates, so I wonder whether he’ll change my mind. He’s certainly thought a lot harder about these issues than I have. I’m also deeply curious to see what he’s like as a person. He’s incredibly open in his books, talking about harsh details of his life growing up and especially about his own extensive use of drugs. My guess is that he’s going to be a lot more fun than my usual guest.

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Steve LEVITT: All right, so let’s start with the punchline. If you were in charge of drug policy in the United States, and you could start completely from scratch, no constraints, what set of policies towards currently illicit drugs would you put into place?

Carl HART: Oh, the first thing I’d do is I would legally regulate the drugs that people seek from cocaine to heroin, to cannabis, to MDMA. People might have to pass a requirement, like a driver’s license, in order to purchase something like heroin and cocaine. And I would also control the unit dose — make sure that there’s not enough in a product to kill people. When we are dealing with the illicit drug market there isn’t any quality control. The substances may contain poisons, toxins, and other impurities that may be dangerous to the person.

LEVITT: Anything else goes with that?

HART: We’d have to change what we do in terms of public education. For example, we would have to have public service announcements that would be helpful in teaching people how not to mix certain drugs, warning people about the potential dangers for overdose there. But also giving realistic education, understanding that some drug mixtures are actually desired, like a sedative and a stimulant or like a speed ball. Just warn people about routes of administration. If you snort a drug, it kind of functions as a safety mechanism, as opposed to smoking a drug where you can put as much as you can or want into your bloodstream. And that’s where people get into trouble.

LEVITT: So I’ve read your book Drug Use for Grown-Ups, which is a new book — excellent book. And you really are in favor of a lot of drugs that a lot of other people aren’t in favor of. Are you the only person on the planet who’s singing the praises of opioids and crack cocaine and methamphetamines these days?

HART: Maybe I’m one of the few people who is willing to acknowledge the benefits of these drugs. But there are a number of people who privately acknowledge the benefits. I mean, they use these drugs. And so it’s O.K. right now in our society to acknowledge psychedelic use, because it’s hip, cool. It’s associated with our educated class, associated with white members of our society. And so that’s so easy. But when you think of something like heroin or methamphetamine, now you’re talking about the lower classes of society, the undesired people. And when you are standing up for the undesired, it’s a lonely place to be, but it’s the right place to be and history will show that.

LEVITT: So in your book, you mentioned that you use heroin. And there must’ve been a hundred headlines about “Columbia Professor Admits to Heroin Use.” Did it surprise you how the reporting went about that issue?

HART: Hell yeah, it surprised me. The thing about it is that I acknowledged psychedelic use, MDMA, but the only headline was heroin because heroin, of course, is the scary, evil, boogeyman drug. And also, people knew that it would enhance the clickbait potential of their headlines. Actually, it pissed me off because what it did was got in the way of the book’s message of being loving, being magnanimous, caring, open, and in expressing some sort of compassion for people who were getting their asses kicked in this society. But how I have been treated has been really rewarding at some level because of the hostility. It gives me an opportunity to see how other people are vilified, not talking about drugs, but just for other reasons. I feel a real kinship to people who were gay in the 1960s, early ‘70s when they were vilified just for being. It’s nice to be someone who is vilified openly, like I’m a Black man in this society — it happens a lot more subtly, but it happens. Whereas with drugs, you’re permitted to say all kinds of awful things about someone just because they are identified as a drug user. For me, it’s a good thing because really, I’m good. I am cognitively intact. I have a middle-class income. I have a home. So I needed to have people attack me like that so I can have more sympathy for other people who are being attacked and they don’t have the resources that I have.

LEVITT: So let’s backtrack a little bit because I wanted to jump in right into the bottom line. So people understood what you were arguing for. But whenever I think about public policy, I like to make a sharp distinction between the set of facts and the conclusions that are drawn from those facts. And facts are presumably things that everyone can agree on. And then conclusions, sometimes reasonable people don’t agree on. You’re a scientist, and I just wanted to give you a chance to rattle off some of the facts that underlie the position you’re representing about legalization. Because I think even if you don’t convince everyone of your conclusion, I think your facts are really powerful and they might move people part of the way, open them up to some ideas they wouldn’t otherwise.

HART: One of the most important facts is the promise of the country — the original promise that is laid out in the Declaration of Independence that each of us have the right to life, liberty, and the pursuit of happiness so long as we don’t prevent other people from enjoying their rights. And so as part of that, it’s incumbent upon any nation that claims to be as free as us to make sure that these things are legally regulated. Otherwise, how can you be preventing people from putting what they want in their own bodies if they’re not bothering anybody?

LEVITT: I find it an interesting lead for you as a scientist, because I would have expected you to get all geeky and to start talking about the studies you’ve been doing in your lab. I’m surprised that you would lead with a libertarian argument. Not that it’s a bad argument — I’m used to libertarian arguments at the University of Chicago Department of Economics.

HART: The scientists who participate in this endeavor, they may not come down on the same conclusion as me. But the fact is we give these drugs in the laboratory to people every day, we give thousands of doses of these drugs on a yearly basis without incident. And if these drugs are so dangerous we wouldn’t be permitted to do the thing. That’s a fact, if you look at the scientific literature, but I wanted people to think about what it meant to be an American. I mean, you see these people with these damn lapel pins and their flags, but not understanding what it means to be an American. And that’s the original promise. That’s the original document. So when people say it’s a libertarian argument, it’s not a libertarian argument, it’s an American argument.

LEVITT: So you talked about the pursuit of happiness in the Declaration of Independence, and as I’ve studied drugs on and off over the last 20 years, what’s been clear to me is that people think that the happiness you get from drugs — they treat that as illegitimate. It’s just an observation I’ve had, which has always made me wonder — because as economists, we treat almost every kind of source of utility as equally good as the next one. It’s O.K if you like opera, it’s O.K. if you like jazz, it’s O.K. if you like metal. But an undercurrent of the discussion of drugs is that’s not real happiness. That can’t be counted. We don’t add that up in our social utility function. What do you think of that argument?

HART: You’re absolutely right. This idea that one has to earn pleasure. Pleasure from drugs are seen as unearned pleasure, which is this ridiculous notion. That’s what I was trying to do. I was trying to write a book about drugs and pleasure and I kept getting sidetracked with these adolescent arguments about — what about the children? What about addiction? And I tried to point out that addiction and those other negative effects represent a relatively minority of effects when you think about the broad range. And so I was trying to have some balance. But people want to always bring you back to the negatives, the harms. And if you’re not exaggerating the harms or stressing the harms, then you’re considered irresponsible when you have these drug discussions. It’s maddening as a 54-year-old adult in this country. It’s like, “My God, I want to have an adult conversation about this.”

LEVITT: O.K. So let’s agree on our first fact — that drugs make people feel good —  and you have a lot of evidence from your lab to support that.

HART: That’s right. If you look at the scientific literature when these drugs are administered, the predominant effect is euphoria, pleasure, alertness in many cases, improvement on performance in terms of cognitive performance, increased social interactions — all of these sort of beneficial effects that we get from drugs.

LEVITT: You would argue based on your research, I think as well, that there are many people who use drugs regularly that are highly functional adults.

HART: That’s right. The vast majority of people who use drugs regularly in the United States — as we define regularly as once a month — there are about 35 million Americans who report using drugs regularly. Now, that means that there are far more than that. But 35 million report it.

LEVITT: And the fact people cite on the other side is that there’s a whole bunch of folks who are being hurt by these drugs in the end. Going to facts again, what share of regular users would fall under the category of, I don’t know, abusing or addicted — I don’t really know what those different words mean officially in the literature.

HART: Yeah. So let’s just define that now. So when I think of addiction I am referring to the DSM-5’s definition. That is the Diagnostic Statistical Manual of the American Psychiatric Association. And it’s where you have psychosocial disruptions or disruptions in your ability to meet important obligations: work, family, educational obligations, and so forth. And another component is that you are distressed by these disruptions. So that’s what I mean when I’m talking about addiction. And when we think about the percentage of people who meet criteria for addiction, it ranges anywhere from 0.5 percent to 30 percent. So we think about a drug like tobacco, a third of tobacco users will experience addiction at some point. Heroin users, about 25 to 30 percent will experience addiction at some point in their life. Cocaine about 15 to 20 percent, alcohol about the same numbers. Cannabis about 10 percent. So you can see that the numbers may range based on the drug, but the overwhelming majority of users of any drug do not meet criteria for addiction.

LEVITT: And you also have argued that — let’s just say the fact is that many people abuse drugs have other problems going on in their life. Let me stop short of making a conclusion about causality. Some people argue the drugs are causing the problems then other people argue the problems are causing them to abuse the drugs. I think we can all agree though that in the literature, there’s a lot of evidence that having other issues is a strong predictor of abuse.

HART: That’s right. A large percentage of people who meet criteria for addiction, also meet criteria for depression, anxiety, schizophrenia, and other psychiatric illnesses. A large percentage of these people also are having problems with unemployment or underemployment. A lot of these individuals have problems with unrealistic expectations heaped on them. So a number of these sort of factors correlate with addiction.

LEVITT: Another point I think we could agree on, you and I, is that the criminal justice enforcement of drug probation falls heavily on minorities.

HART: Yeah. So it’s not minorities, it’s a select group of minorities. So it’s Black people and a select group of Latinos, like Mexican Americans, Puerto Rican Americans. Those are the ones who are really catching hell.

LEVITT: So, let me make a thought experiment. Let’s say we followed your plan. We legalized all these drugs in a regulatory environment, and let’s just say to make it simple, the price was basically zero — close to zero so that you didn’t have to worry about black markets and violence related to black markets. How many Americans would you guess — so now we’re out of facts, we’re into educated guesses. How many Americans do you think would be abusing or addicted to drugs in that world? And how many drug-related deaths would you predict would happen in the U.S. each year?

HART: Well, I think that our drug-related deaths will go down, definitely. Because many of these deaths are caused by tainted drugs and ignorance. And also people will be less likely to feel embarrassed or the stigma associated with drugs would also be decreased. And so people can seek information. And then we would require our medical community to be better informed because the medical community is part of the problem here in terms of their own ignorance about these things. So I think the numbers of overdose deaths related to the recreational drugs will go down.

LEVITT: O.K., let me stop you there. Cause I think that’s really interesting because that’s a case where if we asked one of your rivals in your discipline, they’d probably say “No. Use might be five times greater. And so deaths might be five times greater.” Now I’m sure that would be an exaggeration, but it’s one of those questions we don’t really have — maybe we do, I should ask you. Do we have any way other than introspection to get insight into this, I guess Portugal’s —

HART: That’s right.

LEVITT: — an example. Portugal decriminalized, I think, all drugs, it must have been almost 20 years ago. What’s happened in Portugal?

HART: That’s exactly right. The overdose rate dropped significantly in Portugal when they implemented decriminalization. People sought treatment. All of these pro-social things increased.

LEVITT: Everything we’ve talked about so far, if I take an unbiased view, like literally everything we’ve talked about supports your argument. Now, the one big chink in the armor that I see is those numbers you gave about addiction and abuse because I think people who are against legalization, they’re just going to say, “Look right now, 30 million people use drugs. If you legalize it, every teenager is going to at least try drugs. And people don’t have a very good idea of who’s going to get addicted or not. And so a bunch of kids — 10 percent of all the kids in America — are going to end up addicted to these drugs and ruin their lives.” Do you have a good counter argument to that?

HART: That’s some stupid sh*t. This notion that we should somehow ban an activity because we are afraid of kids engaging in that activity. We should ban cars because we’re afraid of kids driving cars or sex because of sexually transmitted infections. That’s a really ridiculous notion, but we all play into it. Parents still have to parent, and these drugs are still illegal for kids to use and purchase. It annoys me when the kid argument is thrown into the mix, because what it does, it immediately shuts down any sort of rational adult conversation about these things. And we do, by the way, have pretty good information about the likelihood of who will become addicted and who will not become addicted. If you have someone who does not have well-developed responsibility skills, that person is overtaxed with expectations and unrealistic expectations, the person has psychiatric illnesses, or physical pain, has recently lost a middle-class paying job — all of these things certainly increase the likelihood of somebody meeting criteria for addiction. One of the reasons that I came out about my own drug use is that I don’t worry about me ever becoming addicted. I assure you that won’t happen. Because I have all of these responsibilities that I love taking care of. And I also know that people would love to see me have an addiction problem, so they can say, “Ah, see, there’s a cautionary tale.” That challenge I welcome. But we tell people this nonsense, like “You don’t know who’s going to become addicted.” That’s bullsh*t. We do. And those are the same people who get in trouble with a number of other issues in their life.

LEVITT: O.K. But let me say, I think you’re being a little misleading with the automobile example because look, you’re all about trade-offs, I’ve read your research and you do this fascinating research where you bring heavy users of drugs, like crack into the lab, and you give them a choice between taking a hit of crack now or getting a voucher for money in the future. And one of the most interesting things you show is contrary to everyone’s belief these heavy users are able to make sensible trade-offs and they view drug use and the pleasures from it, as fitting into some bigger hierarchy of needs and wants. So I think it’s disingenuous to talk about automobiles because, obviously, automobiles provide a huge positive benefit. And so we take the hurt that comes with crashes with it.

HART: Because automobiles are necessary, right? That’s what you’re saying?

LEVITT: No, I’m saying that without automobiles, life as we know it would be hard to accomplish. And of course, there’s this devastating tax that comes with automobiles of maybe 30 or 40,000 people dying per year in crashes. But if you put like the actual risk of a person driving a car of dying in a crash it’s not vanishingly low, but it’s really low because we spend so much time in cars. It seems to me somewhat unscientific to say, “Look, we tolerate deaths in cars, so why shouldn’t we tolerate deaths from drugs?” And I think people could very reasonably say, “If you can show me the benefits of drugs are high enough that the cost of addiction is vanishingly small compared to the benefits, then that makes sense.” But I think we’re in a very different territory around drugs. And, I mean,  I know you’ve got a point, like you’re fighting against an army of people who are using every tool they have to keep drugs illegal and whatnot. And so you’re probably willing to use whatever tactic you have. In some sense, you’re an advocate, you’re an academic and you’re an advocate. And I was just trying to get the academic part separate from the advocate part.

HART: No, it’s a great point. I mean, when we’re talking about just the relative numbers of people who are in automobiles, there’s a relatively small number of people who die from car crashes compared to the relatively small number of people who use drugs. And then the numbers who die from drugs. Yes. That’s what we’re saying.

LEVITT: Yeah, that was the point I was trying to make.

HART: It’s a good point. Now, just to be clear, I’m not talking about addiction here. I’m talking about overdose deaths because the people who are addicted are less likely to die from overdoses. It’s the people who don’t have tolerance and people who are relatively inexperienced who are more likely to die. And the point that I was making was not to say that we have a comparable comparison because you are right, when you talk about the relatively low number of people who die in car crashes. The point was that life is not without risk. And if we think about skiing, we think about a number of these activities where people get injured — professional football — we tolerate those sort of things because it’s part of being a member of the human society. We acknowledge these risks all the time. We make these risk to benefit calculations as we go throughout our day. But somehow we have treated drugs as special. And even in this conversation, like you talked about addiction and overdose like they’re one in the same and they’re very different things. The overdoses come primarily from ignorance and they also come from suicide. Few people are talking about drugs like Gabapentin, a nerve pain medication, or about antidepressants, a number of these drugs that always show up in the person’s toxicology who has died. We oftentimes talk about the opioids because that’s what’s sexy right now.

You’re listening to People I (Mostly) Admire with Steve Levitt, and his conversation with neuroscientist Carl Hart. After this short break, they’ll return to talk about Carl’s lab-based research.

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LEVITT: Today’s listener question comes from Shane. And Shane writes, “I am a high school math teacher in the state of Virginia and the state is getting ready to do a major overhaul of the math curriculum called Virginia Mathematics Pathways Initiative. One major component of this is that when students enter 11th grade, they are required to choose from one of five different paths of mathematics. I’m very excited about this new opportunity for our students,” Shane writes, “But there’s one thing that gives me pause. We don’t teach students how to make important choices. Do you have any recommendations about how to prepare students to make such an important decision?” So, Shane, let me start by saying — hats off to Virginia for shaking up the way we teach high school math, that’s an issue I’m extremely passionate about. And if people want to know more about my thoughts on that topic, they can listen to a Freakonomics Radio episode that I guest-hosted. It was episode 391 and it was entitled “America’s Math Curriculum Doesn’t Add Up.” Now, let me turn to the question of decision making. So, Shane, I’m not sure this answer will be very helpful to the students of Virginia, but let me at least describe how I think about making decisions.

Now, I want to divide my answer into two pieces. So there are situations where you have really good information about a decision, but it’s still really hard to make a choice. And there are other cases where you’re either too distracted or too lazy or so uninformed that it’s hard to even gather information and then you know you can’t make a good decision. Let me start with the case where I don’t have good information and I’m also not willing to invest the effort to get good information. So in that case, the typical path that people follow is to hire an expert. So when I’m selling my house, I might hire a real estate agent. If I’m thinking about investing money, I might hire a financial adviser. O.K., and that’s not the worst thing you can do, but you have to be really careful in thinking through the incentives that the expert has and how they’re not the same as yours and how that can distort the advice that they have. Now, you don’t know very much so you’re really at a disadvantage. And as we write about in Freakonomics, oftentimes these experts will therefore take advantage of you. So I don’t actually think that’s usually the best advice.

The better option, if you can, is to find a friend or a family member or colleague whose opinion you trust, who, unlike you, is not so lazy and distracted that they’re unwilling to go and gather the information to make a good decision. So I try to find someone who’s faced the same decision as me, who I know and I like, and then I just do whatever they did. If it was good enough for them, it’s probably good enough for me. Now let’s take the other situation, and that’s where you actually have good information and you’ve thought really hard about a problem and you can’t figure out what to do. Now, one rule of thumb I use in that case is I think about the worst case scenario, because for me, I find that regret is a really painful, sticky emotion. So I get over anger and I get over sadness. But regret can stick with me for years, even decades. So what I do is I think about the two choices that are in front of me, and I try to imagine the worst case scenario. And I think about “In that worst case scenario, if I make this choice, how regretful will I feel?” And then I take whichever choice leaves me feeling less regret in the worst case scenario. I don’t know if that’s a good rule or not, but it’s one that I use.

Now, let’s say even after I’ve gone through that regret exercise, I’m still not sure. In that case, I think very good advice is to take whatever path is the biggest deviation from the status quo. So I’ve actually done research in this area, and it turns out that the people who make the biggest changes end up reporting being happier six months later. And it’s not just correlation. I’m actually able to randomize to a certain extent who makes these different choices. And the people who are randomized into making a big change are on average, happier than the people who aren’t. So, if you can’t decide what to do, follow the path that’s the biggest deviation from the status quo. So, that’s how I think about making decisions. But I’m also interested in how you all think about making decisions. Let me know your approach. You know how to reach me — it’s And I look forward to hearing your ideas. Let’s get back to the interview.

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LEVITT: I cannot remember the last time that I raised a point in a discussion and someone’s response was, “that’s some stupid sh*t.” I love that he said that. I wish people would do that more often. Ever since Freakonomics came out, people act like things I say are brilliant, even when my points are trite or even worse, when I spout stupid sh*t. It’s so refreshing to get an honest opinion. In the rest of the interview, I’m going to first try to learn a little more about his research lab and then get into some more personal topics like what pushed him from research into advocacy and what’s it like for him to be at the center of a firestorm of controversy over his new book. 

LEVITT: Can you tell me about your lab? What kind of studies do you run there?

HART: We run studies where we call them human behavioral pharmacology studies, where we give doses of these drugs, like MDMA, methamphetamine, opioids, cocaine, marijuana to research participants and we study the acute effects, the immediate effects, as well as the long-term effects on things like cognition, social interactions, sleep, food intake — a wide-range of effects. We do this work to create a human database for what these drugs do and what these drugs don’t do. And as a database, hopefully we’ll also help inform treatment. It will help inform conditions under which you can expect to get positive effects versus negative effects. It used to be quite fun doing this research.

LEVITT: What do you mean used to be?

HART: In the course of writing this book, I traveled and I got high with a lot of people around the world in natural settings. And I saw how people do it in the real world, as opposed to what I read in the scientific literature or what my colleagues and I may have thought. And people do a lot of drug combinations. They do ketamine in combination with cocaine. They do opioids in combination with sedatives. In the laboratory we tend to study single drug administration. So, one drug at a time. It’s important, of course, but I like to increase the doses that we give in the lab. And I like to also study drug combinations and it will really be nice to study more intimate interactions or sexual interactions after drug administration.

LEVITT: I’ve heard that context — and you just alluded to this — I’ve heard that context matters so much with drug use, that heroin users get a different high, if they’re alone in a sterile hospital room versus in their apartment with friends. That must pose a tremendous challenge to the kind of research you’re trying to do.

HART: Yeah, context is everything. And in the book I describe how I did a study in which we compared the effects of methamphetamine with the effects of MDMA. When you look at the chemical structure, methamphetamine versus MDMA, the chemical structures are nearly identical. There is a dioxy ring on the MDMA structure that is not on the methamphetamine structure. That’s the only sort of difference. And based on our measures in the lab, the setting and so forth, we concluded that they produced a lot of overlapping effects and they produced similar effects. And there were very little unique effects produced by either drug. And you might come away thinking that, yeah, they’re about the same. But when you get reports about the drug effects they differ widely. And so my wife and I did an experiment where we did the same sorta thing in a setting that we were comfortable in and they produced wildly important, different effects. MDMA of course produced more intimacy, more empathy, openness. Although methamphetamine was quite good, but MDMA was unmatched. So that just highlights the importance of the setting. And it also highlights the importance of some anecdotal reports because anecdotal reports too, can be quite informative.

LEVITT: So every university has a human subjects’ committee whose express purpose is to protect research subjects from harm, but whose actual activities are primarily to make the lives difficult for researchers. Do you fight a lot with your I.R.B.?

HART: No, I’m on the I.R.B. myself. We have quite a bit of experience at Columbia with these drugs. You see again, this belief that these drugs are so dangerous is so pervasive in our society, people might think that we would have a difficult time with our I.R.B. but not really. Just think about it, in America we still give electroconvulsive shock therapy to patients — E.C.T. We have a lot of research studies that use that technique. For me, that’s far more dangerous than giving someone a drug and there are a lot of potentially dangerous things that happen in the course of research. A lot of things that are more dangerous than the drugs that we give. I mean, antipsychotic medications. Give me heroin any day before you give me Haldol or one of these antipsychotic medications. Even the anti-depressants, some of those. Give me cocaine or amphetamine before you give me one of those drugs. But the way we have vilified these drugs in our society, lay people think that these drugs is far more dangerous, and they are deluded.

LEVITT: It’s interesting to me that when you came into this profession, you didn’t have the same views you have now. Over time, you’ve really switched your views. How’d that happened?

HART: Well, I came in during the late ’80s, early ’90s, where we were all worried about crack cocaine. And I tried to be a good community member. I came from a predominantly Black neighborhood, resource-poor, but rich in all kinds of other ways. And so I wanted to contribute to my community. And so I studied drugs, the neurobiology of drugs, and I wanted to figure out a brain mechanism that I could tweak and help people who were suffering from drug addiction. And I figured that if I could contribute in that area, then I could help solve some of the problems in my community because I thought the problems were caused primarily by drug addiction. Over time I learned that I was wrong. And this is part of me expressing that I was wrong and trying to help the society do the right thing. And that’s why I have taken this position, like you said, as an advocate. I am an advocate. I’m a scientist, but I’m also an advocate.

LEVITT: So was there some event that flipped you towards advocacy? Because I read your first book, which is called High Price, which is kind of a biography and you were the nerdiest lab rat that ever existed. I would’ve never imagined you emerging as an advocate. Did something happen or it was just an evolution?

HART: I just think it was an evolution. You know how it is. We go to scientific meetings and conferences and then you start to notice people over-interpreting data in this era — I’m talking about the early 2000s — brain imaging findings were sexy and they were everywhere. And so I would go to these conferences and see how people were interpreting small differences, but their interpretations were so wildly different. Some small difference in the drug using population was interpreted as some important, major difference that controlled behavior. When, in fact, it looked just like the control group. I like to focus on the methamphetamine work in this area. People have looked at methamphetamine users or the brains of methamphetamine users and compared those to the brains of people who’ve never used a drug. And you might see that some area in the prefrontal cortex is smaller in methamphetamine users compared to folks who never used the drug. That’s when we look at the means of the two groups. But when you look at the individual data, say if you have 15 to 20 participants, many of the folks in the methamphetamine group look exactly like many of the folks in the control group. And you might see one or two outliers that are pulling the averages away from each other, yet we make a big deal about this small difference. The difference might be statistically significant, but when it comes to function, the two groups function exactly the same. When you give them cognitive measures, their performance is within the normal range of functioning. When you start to see that over and over it started to feel like this had become dogmatic. And it became very clear that we were biased. And that really annoyed me because I thought science was the great equalizer. That is, the person with the best evidence wins.

LEVITT: Could you say one other thing related to that, Carl, which shocked me, is that so many of these studies are cross-sectional in the sense that they look at people only once and they compare the group that’s a heavy user of methamphetamines to those who don’t, without any knowledge of what their brains might look like beforehand — that might’ve led them to use the drug in the first place.

HART: Yeah. So in chapter four in the book, the brain chapter, I ask the reader to pay attention to the language that’s used. Oftentimes researchers use language like “drug users’ brains have atrophied,” or “you see this decrease in volume.” Yet, they only took a measure of the person’s brains one moment in time. And so they can’t say anything about a change, but oftentimes they do. And that’s a clear violation of what they can actually say with their current methods.

LEVITT: And that’s a great example of not making the distinction between what the facts are and what the conclusions are. The facts are that in a cross-section there are these differences between the methamphetamine brain and the non-user brain. And it turns out that empirically they’re small and that you know nothing about the causation, because there’s no randomization, there’s no before and after. And I think those kind of conversations — where people aren’t clear about what the facts are and jump right to conclusions — they’re the bane of public policy discussions.

HART: That’s chapter four. The entire chapter is designed to give the reader some basics about brain imaging and to show the reader how brain imaging findings are being used in order to manipulate the public’s view of drugs.

LEVITT: And what do you think the people in your field who are making these exaggerations — what are they motivated by? Is it academic return? Are they confused? Is it ideology? What do you think’s going on?

HART: I don’t think it’s intentional. So, I just want to be clear — it’s just what’s expected. When you do a study, you are expected to have a finding. And so you torture your data to death to find that finding and that finding oftentimes is shaped by the mission of your funding agency. And our predominant funding agency is the National Institute on Drug Abuse, whose mission is to focus on, almost exclusively, the negative effects produced by drugs. And so we as researchers, we conform to their mission. The journal editors also get grants from this agency. The reviewers also receive grants from the National Institute on Drug Abuse. And so we’re all in our bubble and this bubble is biased.

LEVITT: I can’t tell, now that you’re doing advocacy, whether you’re doing it because it’s fun or whether it’s the ultimate act of self sacrifice, because you’re, obviously, being vilified by all sorts of people. I’m sure everyone in your profession despises you for what you’re doing. But some people really like to be on that pedestal — they like the attention. Is it fun, or no?

HART: No. No, man. I’m a private person. I really do like my privacy. Particularly, if you’re going to be using psychoactive substances that are banned you should be private. But the bottom line, man, it’s that this is wrong. I was raised to stand up for the underdog, the folks who were getting their asses kicked unfairly. I thought that was quintessentially American and that’s why I’m so surprised more people in the field haven’t spoken up. But I’m a Black man in America. I have Black boys who are targets of this drug war, who will be potential victims of this drug war. What kind of man would I be if I didn’t stand up when I know this is wrong? For example, in the book, when I talk about the brain imaging chapter, I challenge anyone to go through that chapter and to rebuke anything I said about the brain or to point out something that was inaccurate or misleading or intentionally biased or something. My science is tight and people in the scientific community know this. I find the ones who are quiet, I find them to be disgusting and I am upset with them. But I don’t want to be out here. This ain’t comfortable.

LEVITT: For me. it has been absolutely shocking. The change in perception around marijuana that’s happened in your and my lifetime. I think the approval rates on marijuana have gone from 10 or 15 percent when you and I were kids to 60-something percent now. Does it surprise you that transformation happened and does it make you hopeful that same kind of transformation might be in the offing for other drugs?

HART: Knowing what I know now, it doesn’t surprise me. Knowing in the early 1970s, for example, the numbers of Americans who said marijuana should be legal, was fairly high as well. In fact, a number of states decriminalized in the ’70s —  New York was one, a number of other states decriminalized — because of this high rate of Americans saying that the drug should probably be legal. And then, late ’70s, early ’80s, the tide changed. And then that’s when we had the lower approval rates. And so knowing what I know now, I’m surprised it took so long, one. And I’m also surprised that we still hold these misinformed tropes, anecdotes, about other drugs. I’m surprised that people haven’t said that, “If we were lied to about marijuana, could we have been lied to about these other drugs?” And people haven’t made that step.

LEVITT: I feel like you’re just at the beginning of this fight. What are you going to do next?

HART: I’ve said everything that I want to say about drugs in this book. And what I want to do is go and enjoy my life, my wife, and be psychoactively altered when I choose. And watch our children thrive. That’s what I want to do. I’ll help where I can in society. And I’ll speak up where I have something to say about injustices, but I really just want to be left alone, to be honest with you, man.

LEVITT: I have to say, I found Carl’s argument surprisingly persuasive. I’ve always been in favor of legalizing marijuana and against legalizing harder drugs. Now, I’m not so sure. I’m still a little worried that the number of heavy users would explode if we legalized hard drugs. But maybe in a world where there’s easy access to cheap, medical-grade drugs, even that isn’t the end of the world. I wouldn’t have said this an hour ago, but I think it’s time for Oregon or Colorado to lead the charge and serve as a guinea pig for legalizing all drugs. 

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People I (Mostly) Admire is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, No Stupid Questions, and Sudhir Breaks the Internet. This show is produced by Freakonomics Radio and Stitcher. Morgan Levey is our producer and Dan Dzula is the engineer; our staff includes Alison Craiglow, Greg Rippin, Joel Meyer, Tricia Bobeda, Mark McClusky, Zack Lapinski, Mary Diduch, Brent Katz, Rebecca Lee Douglas, Emma Tyrrell, Lyric Bowditch, Jasmin Klinger, and Jacob Clemente. All of the music you heard on this show was composed by Luis Guerra. To listen ad-free, subscribe to Stitcher Premium. We can be reached at Thanks for listening.

LEVITT: Anything that you want me to know before we get started?

HART: Yeah, if you can make sure your listeners buy, like, a million copies of the book that’ll be cool.

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