MS. DIANE REHMThanks for joining us. I'm Diane Rehm. A new report from the National Institutes of Health indicates that a growing number of teens do not believe regular marijuana use is harmful. But Nora Volkow, director of the National Institute on Drug Abuse, warns that regular exposure to the main psychoactive ingredient in marijuana can have a potent effect on the teenage brain.

MS. DIANE REHMNora Volkow joins me in the studio to talk about trends in teen usage and the science of addiction. I know many of you will have questions. Feel free to join us, 800-433-8850. Send us your email to drshow@wamu.org. Follow us on Facebook or send us a tweet. Dr. Volkow, it's nice to see you again.

DR. NORA VOLKOWDiane, thanks very much for having me.

REHMAlways, always. Tell us about this survey. How often is a survey like this done?

VOLKOWThe survey that we do, which is targeted to high school students, is done on a yearly basis, and we survey 42,000 kids around the United States. So it is highly representative of the high school population. There are other surveys. There are other surveys. There's one done by SAMSA, which actually is based on a household report, and that's slightly larger than ours. And there's also a CDC survey.

VOLKOWAnd having access to these three different independent surveys allows us to see if the patterns that we're observing with one are concordant with the other, which actually is important to determine the validity of the information you're obtaining.

REHMI think that was the question I had, how often you assume that teenagers are responding accurately.

VOLKOWWell, Di, it is extremely important. You want to know that you do have data that does reflect what's going on as opposed to reflecting what the teenagers may want you to think that they are doing. And even though you'll never have 100 percent certainty of the accuracy of any type of survey, the fact that consistently we'll obtain similar patterns of drug use and perceptions across the different surveys gives us confidence that they do reflect, to a certain extent, what's going on in the United States among teenagers.

REHMSo, clearly, your report shows marijuana use among these teenagers is up. They don't believe it's harmful. You suggest otherwise.

VOLKOWWell, what the survey is telling us is that only 40 percent of 12th graders believe that the regular use of marijuana is harmful. That's much lower numbers than we used to have in the past, and that has actually significantly reduced the numbers, even from last year. And we know from the survey that the perception of marijuana's harm effects does influence the likelihood of adolescents taking marijuana.

VOLKOWThe greater the number of kids that believe that marijuana's harmful, the lower the number that will try marijuana and vice versa. Now, what we know about the marijuana, as well as other drugs, is that the effects of drugs in the human brain are not the same when you take them as a child, adolescent or as an adult, and this is because there are significant changes in the brain as we go in the transition from childhood into adulthood.

VOLKOWAnd our brain continues to change even as adults, but the largest amount of changes really are occurring during those developmental stages, which, of course, leads the brain to function in different ways and respond to stimuli, including drugs in different ways. And whereupon someone says, well, there's no harm or smoking marijuana as an adult here and there, you cannot extrapolate that necessarily adult to the adolescent brain.

VOLKOWAnd this also pertains to other drugs, but we're speaking of marijuana. And indeed, what's very salient, certainly, for marijuana is that, again, we're speaking about the biology of the brain itself. What do we know? Marijuana, one of its main targets, recognized targets, are through the cannabinoid receptors. And the main target in the brain for the cannabinoid receptors is cannabinoid receptor 1.

VOLKOWAnd the concentration of cannabinoid receptors in the brain varies during these developmental stages and this concentration in different areas of the brain also varies. And by the way, it's high, high levels all over the brain, but there are some areas that have higher levels than others. Among the very significant pattern of changes is that, during childhood and early adolescence, the receptors in the brain are very, very high, and then they start to decrease as we proceed from adolescence into adulthood.

VOLKOWAnd these receptors are located, among other places, in white matter, which is the area of the brain that allows really the connections between different regions of the brain. The brain functions as a network where communication is crucial, and information passes back and forth. And that's where we have high levels.

REHMSo the question becomes, why do you think teenagers are not thinking any longer that marijuana is harmful? Is it because they see legalization across the country in various states? Is it because they perhaps see parents using it? Is it -- what is changing their mind from the last time this survey was done?

VOLKOWWell, there's been an increased changes in the policy of the country with respect to marijuana, legalization of marijuana as a recreational drug, legalization of marijuana for medical purposes, and this is changing the attitudes across all segments of the population. And there's been a very strong campaign to actually promote the notion that marijuana is not harmful, and we are all susceptible to norms and cultural perspectives.

VOLKOWAnd so, too, the other thing that we can extrapolate from our knowledge of prescription drugs, why adolescents take them, is because they feel that they are less dangerous than regular illicit substances because they are given by physicians. They can treat diseases, and that gives the full security that they are safer.

REHMIs marijuana today different from what it was, say, 15, 20 years ago?

VOLKOWYes, certainly. And this has to do with just agriculture and engineering to get products that are more potent. And so the DEA has confiscated marijuana, and they assess the contents. And, for example, we have seen significant increases in the active ingredient, psychoactive ingredient, of marijuana which is 9-THC and, for example, actually quite abrupt increases. In 2000, the content of 9-THC may have been 6 percent. Now the content is 12 to 14 percent.

REHMReally? It's more than doubled then.

VOLKOWIt's more than doubled within a 10-year period, so...

REHMSo, you know, you can say these things to teenagers. You can talk with them. You can point to the kinds of studies that your institute has done. What can you show them? You can't show them white matter in the brain that they might say is not going to affect me. What can you demonstrate to them as a change in how marijuana is affecting them?

VOLKOWYeah. No, we cannot show them white matter in the brain, but we can show them how changes in the organization and connectivity of the brain can ultimately affect their performance.

REHMGive me an example.

VOLKOWFor example, there was a study, a perspective study, that showed those individual's levels when they were tested when they were 32 years of age, which had been followed since age 13 and monitoring for their intelligence quotient, their IQ prior to initiation of any drugs, and then were followed periodically. They show that those individuals that had smoked marijuana during adolescence had lower IQ than those that did not smoke marijuana, accounting for premorbid function, which was so important about this particular study.

REHMAnd now does that mean if the teenager had smoked it during those adolescent years and then stopped that the brain showed lower IQ later on as an adult? Or does it point simply to those young people who continued to use marijuana through to adulthood?

VOLKOWThis particular study actually showed that it continued even in those individuals that had stopped smoking marijuana. What was the important element on this effect was having smoked regularly, marijuana, during adolescence. And, again, I reiterate regularly.

REHMBut then how can you perhaps filter out for education, for social conditions, for economic conditions? How can you separate out those?

VOLKOWThe investigators covaried by the parenteral economic and educational status to actually take into account some of these effects that are likely to also influence whether you have a chance to have a good education or not. So that's what the may -- particularly these studies have reported similar findings, but the level of control for all of these variables that can influence was not there. So in this particular study, the effects, though not perfect, appeared to indicate that there is an association of declining IQ by those that are smoking marijuana during adolescence.

REHMNow, what about after adolescence and the teenagers? Suppose one takes it up -- and I realize this study didn't specifically focus on this. Suppose one takes it up between 20 and 25. At 35, are there going to be differences that the brain would indicate?

VOLKOWWell, this study then looked at those individuals that had started in early adulthood, and they were unable to see any differences in those individuals that smoked marijuana as adults.

REHMNora Volkow, she is director of the National Institute on Drug Abuse. We're going to take many of your calls when we come back. Stay with us.

REHMNora Volkow is here with me. She is director of the National Institute on Drug Abuse which has just come out with a new report. It was released yesterday indicating marijuana use among teenagers has risen slightly and that these teenagers do not believe that marijuana use on a regular basis is harmful. And here is our first email: "Are the teenagers correct in their assessment that marijuana use is not dangerous? What is the consensus on research? Just because teenagers think it does not make it wrong."

VOLKOWAbsolutely. No. And I have a lot of respect for the adolescent brain in many ways. But we want to think many things that we like, and we still deceive ourselves. There is significant evidence that exposure to cannabinoids or in animal models or marijuana in humans during adolescence is associated with adverse outcomes.

VOLKOWOne of them in terms of potential negative effects is that, by smoking marijuana, you are maybe disrupting this very carefully orchestrated process by which the brain areas get connected with one another, which, for example, has been associated not just with lower IQ but also with significant differences in connectivity in areas of the brain, for example, that are involved with memory, like the hippocampus, or in the main central hub of the brain which is the (word?).

VOLKOWAnd that is going to make the communication different into these regions. Also, when you smoke marijuana, you cannot memorize or learn as you should. And if you are at high school and you need to be educating yourself, that's going to put you at higher risk for actually doing poorly at school. And let me say just a final one. The other issue is that, the younger you start smoking marijuana, the higher the risk not only to becoming addicted to marijuana, but it also appears to increase the risk for addiction of other drugs in adulthood.

REHMAre there any physical changes, external physical changes, that both a parent or a youngster him or herself might be aware of that occur with regular marijuana use?

VOLKOWNot that have been shown. I mean, there are no obvious physical changes that you may perceive like has been documented for methamphetamine with loss of weight. So there's no real way of determining if someone is exposed to marijuana by physical changes.

REHMHere is an email from someone who identifies herself as a drug abuse researcher, doesn't want her name used, says, "Regarding prescription drug abuse, the surveys show stable use during the last several years. But the DEA, the Drug Enforcement Agency, data show that prescribed opiate use has increased fivefold since 1999.

REHM"Prescribed stimulant use has increased 6.5 fold during the same period. DEA sales data are objective, cannot be faked. Current growth rates 27 percent and 33 percent for prescribed opiates and stimulants respectively. Perhaps the government-sponsored survey should be completely revamped. They do not reflect DEA data at all. " What's your thinking?

VOLKOWWell, I don't know where they get the data that the prevalence rates of opioids have as in terms of abuse have stayed stable in -- they are very high. So they haven't increased in the past few years, but they have been increasing over the past decade -- and the same thing with stimulants. And in fact in this monitoring the future survey, we're seeing a significant increase in the abuse of amphetamines, which is a stimulant medication just for the treatment of attention deficit hyperactivity disorder.

VOLKOWWe're also seeing an increase in the number of people that are dying from overdoses secondary to the abuse -- predominantly abuse of opiate medications when usually frequently combined with other drugs. So the increasing prescriptions both for opioid medications and stimulants appear to be associated with an increase in diverse consequences from these drugs, as well as their own diversion certainly from monitoring the future increases in amphetamines were significant.

REHMNow, during the break, you said that marijuana use among teenagers has gone up rather significantly in the last few years.

VOLKOWWell, it's a slow increase, and it's been all in the past five or six years. But to me the most concerning indicator from the survey is that that relates to regular use of marijuana because it's the one that's associated with most adverse effects, which, for 12th graders, that's 6.5 percent. For 10th graders, it's 4 percent.

VOLKOWAnd that -- these are kids that are at school either daily or almost daily smoking marijuana. And that's, I think -- and those numbers have been very high. Considering that we have higher content of 9-THC in marijuana, this is an indicator that we need to take actually quite seriously.

REHMWhat about use of marijuana among adults? Is that also on the increase?

VOLKOWIt is not a significant increase. It's basically pretty stable vis-a-vis the use of marijuana among adults. We have not -- the household survey which is not given by us but by SAMSA has not shown any dramatic increases in the prevalence rate of marijuana use among adults. That indicators though that appear to be increasing somewhat is those that relate to more frequent use of marijuana. So if they ask, have you ever tried it, those have not per se increased. But are you taking it regularly, those are the ones where they are seeing increases.

REHMAnd that increase, do we know how that increase may affect adults?

VOLKOWNo, we don't really know. There's a lot of data out there that has shown that it will interfere -- when you are smoking marijuana, it will interfere with your cognitive capacities. There's no way around it. You want to be able to memorize and learn. Your attention will be disrupted, and your executive function will also be disrupted. Your motor coordination will be disrupted, so you are more likely to get into an accident. The perception of time is affected.

VOLKOWThis has been dismissed because they say, well, that recovers. And indeed most of the studies have shown that if you smoke marijuana and then you stop for one month, there will be recovery. But there is evidence that while people are smoking marijuana and that there are significant cognitive changes that persist days after stopping the use of marijuana. But they will -- most of the studies do tend to show that they will recover.

REHMAll right. So if, for example, a teenager gets behind the wheel and is caught speeding or is in an accident, are there ways of testing for marijuana intoxication as there are for alcohol intoxication?

VOLKOWYes. There are several tests for measuring whether you have cannabinoids in your blood. The problem is that cannabinoids stay in the body for a long period of time. So if you test someone, say, one week after they smoke marijuana, they will be positive. But that doesn't necessarily mean that they were under the influence of marijuana.

VOLKOWThat's not so much the case with alcohol where, because it goes in and out of the body pretty rapidly, you know, that if you have high levels, those are likely to have contributed to the accident. So with marijuana, it's more complicated. And so research has been going to try to get indicators that may reflect the proximity of the use of marijuana.

REHMBecause marijuana in the system would affect one's driving ability?

VOLKOWCorrect. And indeed studies have shown that individuals that are intoxicated with marijuana perform much worse on motor task. And this overrepresentation of people that are -- with positive marijuana among car accidents and fatalities actually.

REHMDr. Volkow, you're up against a huge body of thought and a huge body of behavior that says marijuana doesn't bother me. Marijuana is not addictive. Marijuana does not affect my thinking or my memory because of course one is the worst judge of one's own behavior. How do you -- as the director of this very important research institute, how do you counter that?

VOLKOWWell, I always say that our tools are science or knowledge. And ultimately performing studies that can provide objective evidence of what the drug does and what it doesn't is what we need to present to the public. I guess many times we have had an experience, nothing happens to us and that would lead us then to believe that that is safe. So we need objective evidence that will allow individuals to have the knowledge so that they can make decisions with knowledge as opposed with beliefs. And that is our task (unintelligible)...

REHMAnd, of course, as states across the country open up their own citizens and their publics to use of marijuana legally, aren't you going to be fighting a losing battle as far as teens are concerned?

VOLKOWWell, it is -- we've never been in a situation really where we have an illegal drug from the inception that we're transferring it into a legal status. Alcohol was legal, then illegal and then legal. But it was legal at the beginning. So we really do not know what is the landscape going to be. We can try to predict. So what we are trying to do right now is requesting researchers that are in states where the marijuana has been legalized to actually evaluate indicators that may tell us whether the changes are affecting negatively in any way or not.

VOLKOWFor example, educational achievement, visits to emergency rooms, visits to treatment programs, criminal acts, accidents, those indicators that can give us an idea of these policy changes to translate into an increase in the adverse effects from the use of marijuana.

REHMTell us about synthetic marijuana and how different that is from the "real stuff" and how its effects might be somewhat different?

VOLKOWSynthetic marijuana in a way is misnomer. It's a synthetic cannabinoid. And marijuana is one of the cannabinoids. And, well, synthetic marijuana or synthetic cannabinoids are about -- are chemicals that have been actually developed to maximize their potency, that is, their effects on the cannabinoid receptor that is associated with the rewarding effects of marijuana. As a result of these, these synthetic cannabinoids are actually significantly more potent than marijuana itself and therefore, not surprising, associated with many more adverse medical consequences.

REHMNora Volkow, she's director of the National Institute on Drug Abuse. And you're listening to "The Diane Rehm Show." What about teenage drinking?

VOLKOWTeenage drinking has actually positively gone down. I mean, it's not very fast decline, but it's significant. Over the past 10 years, we are seeing a decline in the rates of teenagers drinking and getting drunk and binge drinking. So it's a very positive indicator. It's still very high.

REHMNow, those are teenagers as opposed to college-age youth?

VOLKOWMonitoring the future only basically evaluates large numbers, teenagers. And we have, for example, the -- teenagers abuse alcohol a lot, so the prevalence rate for past year of use of alcohol among 12th graders is 62 percent. But it was significantly higher in the past. So it's positive, but we still have a lot of work to do to decrease drinking among adolescents.

REHMAnd what about cigarette smoking?

VOLKOWCigarette smoking, I mean, these are really very positive indicators. And I always like to highlight them because we are seeing, over the past ten years, more than a 50 percent decrease in smoking among teenagers. And interestingly they're using the teenagers and increasing the number of them that are perceiving tobacco as harmful so just seeing this discrepancy on one versus the other. And I'd like to highlight that because there has been a very, very aggressive campaign towards decreasing smoking in adolescents, decreasing drinking in adolescent, and it has paid off.

REHMAnd then what about the painkillers like Vicodin?

VOLKOWWell, we had seen numbers, for Vicodin particularly, quite high for many years at 10.5 percent. And this year we saw a dramatic decline. So from 10.5 for many years it had gone to 7.6 or something. And this year is 5.3 percent for past year indicators of Vicodin use among 12th graders. So it's a very significant decline.

REHMHow do you account for that?

VOLKOWThere's been a very strong campaign from multiple agencies, as well as education towards the recognition that pain medications can be as harmful as elicit substances when used outside of the medical context, and/or when combined with other psychoactive drugs like alcohol or sedatives.

REHMAnd I gather it can cause heart problems, can cause psychotic outbreaks?

VOLKOWWell, opioid medications -- the main problem with opioid medications, first of all they are highly addictive. But the other one -- the main concern is that they are not very safe vis-a-vis overdoses. So the doses that you prescribe are not so far away from the doses that if you take may result in respiratory depression. And then if no one intervenes, you may die because you stop breathing. And that's the cause of overdoses. And it has been significantly increasing in our country. And this, I think, has been one of the wake-up calls. We do have a problem of prescription opiate abuse.

REHMNow, there has been a great deal lately in the press about ADHD and the use of those drugs that have been prescribed in the past. Do you believe they have been overprescribed?

VOLKOWThe evidence suggests that they have been overprescribed. And we have seen basically more than doubling of the prescriptions every decade. Initially it was thought that this was because there was an increased recognition by physicians of the diagnosis of ADHD. But at one time you have to asymptote, and that has an asymptote. And it keeps on doubling and doubling.

VOLKOWAnd if you look at the numbers of the expected number of kids that should have ADHD, approximately 5 to 6 percent, and then the numbers of kids within 7 and 12 years of age that are prescribed, 12 percent, there is a discrepancy that bears examination.

REHMNora Volkow, director of the National Institute on Drug Abuse. Your calls, comments when we come back. Stay with us.

REHMWelcome back. Nora Volkow is director of the National Institute on Drug Abuse. Talking about a new report that NIH released yesterday that marijuana use among teenagers has risen slightly and that teenagers do not believe that marijuana use on a regular basis is harmful. Here's an email from Adam, who says, "To me the real story is that among teens alcohol abuse is down, prescription drug abuse is down, use of tobacco is down. Each of these substances is far more addictive and damaging to physical and mental health than marijuana. It's not even close," says Adam.

REHMHe goes on to say, "From a public health perspective and from the perspective of a father of two, I'll take this trade any day of the week. I only hope the good news continue and that "The Diane Rehm Show" is able to grasp this reality."

VOLKOWAdam and I completely agree with respect to the notion that alcohol and nicotine account for actually a much greater amount of morbidity and mortality associated with all of the illicit drugs. But the reason why they do it is not that they are more harmful or addictive than illicit substances like cocaine or methamphetamine or heroin. The reason why they account for such great numbers is that they are legal. And by being legal, they become widely available. And as a result of probability, if 10 percent of people that get exposed become addicted, your numbers go up.

VOLKOWAnd that's why to me the argument -- I mean, we have the experience, we have the data that indicates that the legal status is associated with a significant increase in adverse consequences. On top of that, I think that when people ask me, which is the most dangerous drug -- they are dangerous in different ways. Smoking tobacco is very harmful for your body, and it produces cancer. Marijuana is harmful in a different way. Its (word?) effects appear to be less than those of tobacco, certainly for pulmonary.

VOLKOWBut it does affect your cognition. And if you are in adolescence and you're studying, I mean, you're going to be stoned -- and I always say, do we want our young people stoned? We want them to learn. We want them to be motivated. We want them to be driven. And curiously, nicotine will not affect cognition. So one needs this argument of which drug is worse -- has to be addressing the context of the differences that each one of them has.

REHMHere's another email from Sam, who says, "The statement that 'the pot of today is much stronger than years ago,' while true, is a red herring if not qualified. The pot of today is also far more expensive and purchased and ingested in ever smaller amounts. If you study the overall amount of THC ingested over the years, I would propose that the amount has been about the same over the years."

VOLKOWWell, this is an important question because that's what some -- people were asking, well, if you have higher content, you will be smoking less and you will basically titrate yourself. And it's a very valid question. So a researcher did indeed investigate these and found that there was a significant increase in the concentration of 9-THC in the blood as a function of the content of 9-THC in the cigarette. So even though there may be some attempt to tritate, the net effect was higher concentration, the higher the content on the cigarettes.

REHMThis email from David ends with this sentence: "Marijuana is not addictive like heroin or even alcohol."

VOLKOWMarijuana is addictive. There's animal models. There's human models. It's actually an addiction that's quite difficult to treat, but -- but, the question is, is it as addictive as heroin, or is it as addictive as methamphetamine? And the answer, I would say no. It's not as addictive as heroin and as methamphetamine, and there are indicators that tell us. So one of them is, what percentage of those that get exposed to it become addicted?

VOLKOWAnd in marijuana, it's 9 percent. If you're an adolescent, it's 16 percent. For a drug like heroin, it's 30 percent. And that indeed gives an indication that, yes, there are drugs that are more addictive than marijuana. But it does not negate the fact that 9 percent of people exposed to the drug, based on epidemiological studies, do become addicted, unfortunately.

REHMAll right. Let's open the phones first to Eric, in Orlando, Fla. You're on the air.

ERICHappy holidays.

REHMHappy holidays.

ERICSo as a physician for 20 years in five different major metropolitan areas, in the ER specifically, my experience has been that the cases that would come into the ER that dealt with all kinds of things from diabetes to alcohol problems, alcohol poisoning and many other things, whether you're consuming trans fats or you're consuming things in an unhealthy diet, there's a disproportionate number of things in our environment that can hurt us.

ERICWe all know this. So I'd the question I'd like to ask is a frame of reference. If your guest could maybe put into some numerical context the dangers of marijuana in direct correlation to many other things in our environment that human beings are exposed to.

REHMAll right. And I presume there he's talking about being overweight, eating the wrong kinds of foods, having high diabetes rates, that kind of thing.

VOLKOWYeah. No -- and the caller -- I wish I had the numbers to give you, but actually, one of the things -- I don't have the numbers, but we do know that the public health problems in our country, the number one preventable one of them is tobacco. And the other one is obesity. So there's no denying at all that these behavioral syndromes, if we want to call them, are associated with very high risks to individuals and very high costs to the healthcare system. The issue is do we want to keep on adding new ones that are going to be associated with a higher rate of car accidents, for example.

VOLKOWThe moment that you legalize these drugs they become more available, more people perception changes, and there's more exposure. There's advertisement. So this is the way that I'll frame it, not which one is worse than the other, but can we afford to have an added one when we already cannot even deal with the healthcare costs that we currently have?

REHMAll right. To Paul, in Miami Beach, Fla. Hi there.

PAULHello. Yes. Cigarettes are being banned, and marijuana is being legalized. The country is absolutely mad. Cigarettes were considered medicinal in the 1920s. They were prescribed for tuberculosis. They believed the smoke in the lungs would kill the bacilli. And, of course, a dram of rum was antiscorbutic against scurvy and forced on seamen in the British Navy.

PAULThey had to have their dram of rum, or else they'd be penalized. So the idea of what's healthy and what's killing changes culturally, but the overall takeaway from this is that America is an empire who's lost its way, where they just don't know the difference between natural and destructive. And if you look at somebody, they're on dope. But it's called getting high.

REHMAll right. Paul, thanks for your call. Dr. Volkow?

VOLKOWYes, indeed. And we have been wrong in the healthcare system. The same thing last century. At the beginning of the century, we were promoting cocaine for a wide variety of ailments, including depression and the treatment of addictions. And then it was recognized that cocaine was very addictive, and it was not helpful in this condition.

VOLKOWSo that is why we have agencies whose function is to evaluate whether indeed a certain intervention is therapeutically beneficial and to regulate that because we all want to believe certain things -- does not necessarily mean they are correct. We need to provide the evidence.

REHMAll right. And to Amrina, in Baltimore, Md. Hi there.

AMRINAHi. So I just wanted to respond to your speaker's earlier comment that making marijuana legal is going to increase use, therefore it's going to cause more detrimental health effects among younger people. And I wanted to say that by legalizing or decriminalizing it, we are bringing marijuana into the same sphere as alcohol and tobacco. And we can then, in a noncriminal way, address the health effects, and we can empower people and have more rich and rigorous conversations around what the terrible health effects are.

AMRINARight now the conversation is -- what kids end up hearing a lot is, it's illegal, it's illegal, it's illegal. Instead, we can have the same degree of deep conversation that we had in this country about tobacco, saying these are the bad effects. And this is what, you know, it causes like cognitive and impairment and we should have deeper conversations with young people and empower them to make that decision and stop making this the drug that puts people on like a trajectory to prison and life that's like…

REHMAll right. Thanks for your call, Amrina.

VOLKOWVery good point. And I actually thank you for bringing it up. Because particularly we need to make, though, a distinction between legalization and decriminalization. So what we have been basically discussing is the potential negative effects of legalization. The issue of decriminalization is a completely different one. And what the data has shown is that drug addiction is a disease of the brain. And that evidently when you have a disease problem you don't incarcerate, you treat. And addressing the notion is the best way of addressing the problem of drugs.

VOLKOWCriminalizing it or addressing it from the healthcare system. And that's a very, very different dialog and a set of responses. I believe correctly that the issue of whether you have someone that is addicted to the drug should be put in prison, may in fact not yield the best results. It could actually be very counterproductive. And I also agree that we need to provide, with the evidence, to young people so that they can make the decisions with their eye wide open and with their frontal cortex in full operation.

REHMNow, of course, you had a surgeon general way back when, 1964, saying cigarettes cause cancer. Cigarettes are harmful to your health. And that's what began that long process. It's the year I stopped smoking. Seems to me if you truly believe that this is harmful, that marijuana is harmful to the brains of adolescents, that same kind of educational program has got to become more widespread.

VOLKOWI agree. And the states that have legalized marijuana, have stated that they will put the systems that are necessary to insure that it does not get into the hands of teenagers. Unfortunately, we know that in the case of illegal drugs and alcohol and tobacco, that has not happened.

VOLKOWAnd we're also observing, for example, in the survey that 30 percent of those kids that report smoking marijuana, in states where marijuana was legalized for medical purpose, 30 percent got them out of marijuana that was given as part of a prescription. So it is very difficult to regulate. We know that we have not been very successful.

REHMAnd you're listening to "The Diane Rehm Show." Let's go to Jack, in Los Altos, Calif. Hi, there. You're on the air.

JACKGood morning. Thank you for taking my call.

REHMSure.

JACKLong time listener, first time caller.

REHMThank you.

JACKAnd I really am enjoying this conversation a lot. Being a teenager in California, growing up, I smoked some pot here and there. I'm a federal officer in the government now. I've gone through college. While I was in college, less than a year ago, I was smoking a lot of pot. I was turning in my assignments perfectly fine. And I really don't think it affected me. It may have affected me cognitively, but I learned to adapt and overcome the situation. And I really do think that it's unfair that the director is looking at -- I think you guys have gone over this and answered the question, so to speak.

JACKBut basically, it's unfair to compare marijuana that's just being legalized now -- it's in its infancy in this country, as far as being legalized, and compare it to alcohol and tobacco, where they've had, you know, millions and billions of dollars of research towards those two products to show that they're harmful. And then the publicity and education efforts to teach kids and the public -- just like you said yourself -- that these things are harmful, and yet still they're being abused and they're highly dangerous.

JACKSo I guess my question is why are we having this conversation and why are we conducting studies when it's in infancy? Why aren't we giving this the chance to be legalized first and then having the cause and effect happen, where we have the education come out of the revenue that's generated from possibly regulating?

REHMAll right. Jack, thanks for your call.

VOLKOWYeah, I mean, obviously all of these issues are complex, but if we look at history to try to actually predict what's going to happen in the past. And with tobacco in 1964, it was actually finally determined that it produced cancer when there was already data that it was harmful and it was producing addiction. And yet it took an enormous amount of time, effort, years and lives lost in order to change that trend. So once you legalize a product, you create invested interests from big corporations that are going to of course be benefitting from the selling of that product.

VOLKOWIt would be very, very difficult to overcome. We are an agency that does science. We provide the studies to try to understand how cannabinoids work, how could using marijuana disrupt the brain? And my view is we cannot afford to do an experiment where people are going to be hurt.

REHMFinally, one last question. "The phrase, regular marijuana use, keeps being used but has yet to be defined to the audience. What is considered by teens as regular use?"

VOLKOWThe descriptor of regular use, as per the survey, we're speaking about the timings daily or almost daily use of marijuana.

REHMAnd there you have it. Last word from Nora Volkow, director of the National Institute on Drug Abuse. Thank you so much for being here.

VOLKOWDiane, thanks for having me.

REHMAnd happy holidays to you.

VOLKOWHappy Christmas and holidays.

REHMThanks for listening, all. I'm Diane Rehm.

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