Casual Marijuana Use Linked To Brain Abnormalities
    By News Staff | April 15th 2014 05:24 PM | 15 comments | Print | E-mail | Track Comments

    Young adults who used marijuana recreationally show significant abnormalities in two key brain regions that are important in emotion and motivation, according to a study in the Journal of Neuroscience.

    The authors document how casual use of marijuana is related to major brain changes and showed the degree of brain abnormalities in these regions is directly related to the number of joints a person smoked per week. The more joints a person smoked, the more abnormal the shape, volume and density of the brain regions.

    "This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences," said corresponding and co-senior study author Hans Breiter, M.D., professor of psychiatry and behavioral sciences at Northwestern University.

    "Some of these people only used marijuana to get high once or twice a week," Breiter said. "People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school. Our data directly says this is not the case."

    Scientists examined the nucleus accumbens and the amygdala -- key regions for emotion and motivation, and associated with addiction -- in the brains of casual marijuana users and non-users. Researchers analyzed three measures: volume, shape and density of grey matter (i.e., where most cells are located in brain tissue) to obtain a comprehensive view of how each region was affected.

    Both these regions in recreational pot users were abnormally altered for at least two of these structural measures. The degree of those alterations was directly related to how much marijuana the subjects used.

    Of particular note, the nucleus acccumbens was abnormally large, and its alteration in size, shape and density was directly related to how many joints an individual smoked.

    "One unique strength of this study is that we looked at the nucleus accumbens in three different ways to get a detailed and consistent picture of the problem," said lead author Jodi Gilman, a researcher in the Massachusetts General Center for Addiction Medicine and an instructor in psychology at Harvard Medical School. "It allows a more nuanced picture of the results."

    Examining the three different measures also was important because no single measure is the gold standard. Some abnormalities may be more detectable using one type of neuroimaging analysis method than another. Breiter said the three measures provide a multidimensional view when integrated together for evaluating the effects of marijuana on the brain.

    "These are core, fundamental structures of the brain," said co-senior study author Anne Blood, director of the Mood and Motor Control Laboratory at Massachusetts General and assistant professor of psychiatry at Harvard Medical School. "They form the basis for how you assess positive and negative features about things in the environment and make decisions about them."

    Through different methods of neuroimaging, scientists examined the brains of young adults, ages 18 to 25, from Boston-area colleges; 20 who smoked marijuana and 20 who didn't. Each group had nine males and 11 females. The users underwent a psychiatric interview to confirm they were not dependent on marijuana. They did not meet criteria for abuse of any other illegal drugs during their lifetime.

    The changes in brain structures indicate the marijuana users' brains are adapting to low-level exposure to marijuana, the scientists said.

    The study results fit with animal studies that show when rats are given tetrahydrocannabinol (THC) their brains rewire and form many new connections. THC is the mind-altering ingredient found in marijuana.

    "It may be that we're seeing a type of drug learning in the brain," Gilman said. "We think when people are in the process of becoming addicted, their brains form these new connections."

    In animals, these new connections indicate the brain is adapting to the unnatural level of reward and stimulation from marijuana. These connections make other natural rewards less satisfying.

    "Drugs of abuse can cause more dopamine release than natural rewards like food, sex and social interaction," Gilman said. "In those you also get a burst of dopamine but not as much as in many drugs of abuse. That is why drugs take on so much salience, and everything else loses its importance."

    The brain changes suggest that structural changes to the brain are an important early result of casual drug use, Breiter said. "Further work, including longitudinal studies, is needed to determine if these findings can be linked to animal studies showing marijuana can be a gateway drug for stronger substances," he noted.

    Because the study was retrospective, researchers did not know the THC content of the marijuana, which can range from 5 to 9 percent or even higher in the currently available drug. The THC content is much higher today than the marijuana during the 1960s and 1970s, which was often about 1 to 3 percent, Gilman said.

    Marijuana is the most commonly used illicit drug in the U.S. with an estimated 15.2 million users, the study reports, based on the National Survey on Drug Use and Health in 2008. The drug's use is increasing among adolescents and young adults, partially due to society's changing beliefs about cannabis use and its legal status.

    A recent Northwestern study showed chronic use of marijuana was linked to brain abnormalities. "With the findings of these two papers," Breiter said, "I've developed a severe worry about whether we should be allowing anybody under age 30 to use pot unless they have a terminal illness and need it for pain."


    “This preliminary study has several caveats. First, the sample
    size does not provide power to examine complex interactions
    such as sex differences. Because this is a cross-sectional study, causation cannot be determined, although marijuana exposure parametrically correlated with structural differences, which suggests the possibility of causation. Longitudinal studies are needed to determine whether marijuana exposure explicitly leads to the differences observed in this study. Furthermore, this study did
    not include quantifiable marijuana metabolite levels, which
    would have provided further information about the amount of
    marijuana exposure. This measure could be incorporated into
    future studies as a complementary measure to detailed timeline follow-back measures of drug use. Finally, age of onset was collected for marijuana use only. Early exposure to alcohol may have also affected brain structure (although no participant met criteria for past alcohol abuse or dependence).” 'Dave'

    I wonder if you told Carl Sagen his brain got bigger after using cannabis if he would agree,,is there any proof that the restructuring is a good thing or a bad thing,,is this the danger that NIDA,the financiers of this study,promised to find since 1974 when they declared they had research that proved cannabis was a dangerous drug and never has had any yet?
    Look to the source please,,it is the same source we have heard all the dangers of marijuana from for the last 5 decades and none have been true.

    You started off okay - this same weak methodology applies to most studies about any product - but then you got all weird and conspiratorial toward the end.

    Your cui bono?/Follow the money logic means Greenpeace perpetuates nuclear power so they can fundraise against it, that Democrats should not trust any science funded by the Bush administration, and is a crippling flaw in every single study in modern times, since no scientist today is independently wealthy enough to be free from corporate or institutional interference.

    Falling back on that is like comparing people to Hitler - it shows intellectual weakness and a lack of a real argument.
    Thor Russell
    Did the study track changes in brain structure with time? Otherwise it may simply be that users with different brain structure to begin with find marijuana  more rewarding their brain structure encourages more risk taking etc. If not then an equally valid conclusion is to say that we can predict based on someones brain structure whether they will take marijuana  at some stage.
    Thor Russell
    "What we're seeing is changes in people who are 18 to 25 in core brain regions [the accumbens and amygdala] that you never, ever want to fool around with," says professor Hans Breiter.
    If this indeed proves to be so, marihuana use might need to be restricted before age 30.

    Agreed. Marijuana is being claimed as some sort of medicine while the harms are being swept under the rug. Like cigarettes or alcohol, it doesn't have to be medicinal but it should be restricted.
    This is most definitely a NIDA funded study as the old, and widely debunked, trope of "gateway drug" is yet again being dusted off. Study upon study shows very few people ever move to harder drugs and of those people it is more about availability than desire to "up the high".

    As for this study, for those seeing alarm bells, it only looked at marijuana use, not any other drug use, such as nicotine, alcohol, prescription drugs, diet, exercise or social health. It's the equivalent to seeing someone trip on something while smoking and immediately blaming nicotine for the accident.

    Next, they make no determination as to whether the changes are healthy or unhealthy or any context in which either could even be determined. They even note the mice study shown increased brain region growth, which could entirely be a great thing. They utterly jump to the NIDA sponsored conclusion of any change being bad and how it automatically makes them a dirty addict looking for a needle to inject. The study shows no such thing or even any indication of any such thing.

    The study showed altered brain formation, that's it. We have no idea if that helps those children feel empathy, experience pleasure, think clearly, learn efficiently, be more creative, more logical, more thoughtful, more impulsive or anything in between. In short, this is yet another example of researchers forcing conclusions from a study which don't exist.

    Whether they overstepped the bounds of their data in order to please their funders or because they themselves are hoping for an addict link is unclear, but one thing is very clear, they have an anti marijuana goal and are stretching data beyond its limits in the hopes of perpetuating hysteria regarding it.

    Until this is further studied, it should go into the "fish oil causes prostate cancer" dustbin. Not to get too conspiratorial, but it is pathetic how quickly media jumps on extremely preliminary research of commonly used substances, due to...wait for it...FINANCIAL INCENTIVE. Cui bono is not Godwin's Law, despite your straw-man attempt to discredit it as a question worth asking.

    can someone who knows more about neuroscience than me explain how a change in structure in these brain regions actually translates over into a change behavior/cognitive expression? This is interesting, why is it assumed that a change is intrinsically negative? Please correct me if im mistaken but according to this write up seems to indicate that the researchers simply found differences in brain structure that may correlate to cannabis use, and it doesnt make any claims as to what effects this structural difference has on behavioral or cognitive functioning correct? So isnt it a bit premature for the researchers to just assume some negative relationship?

    In anycase its interesting research.

    also why is the source just a link to Northwesterns homepage and not a link to the actual article in question?

    Link to article
    and a link to the non-paywalled pdf.

    This is well outside of my area of expertise, but what I find interesting is the automatic assumptions that I am seeing the the comments.  Only a couple of the comments are attempts to discuss the science of the paper itself.  Thor asks a good question, but most want to just dismiss it out of hand because (my assumption here) they don't like the results.

    No one here would argue that tobacco and alcohol are unhealthy for teenagers (and can be problematic for all).  Why the anti-science rants about pot?  If the paper is correct and pot does negatively affect young adults, isn't that something worth knowing? 
    Yes, it's worth knowing about, if you take the abuse of alcohol and prescription drugs just as seriously in young people, especially college age students.

    But it seems that no one has a problem with excessive and even dangerous alcohol consumption on campus, but somehow marijuana still brings out the torches and pitchforks.

    Whenever someone rails against the dangers of fast food in children, the argument is always about how people should have the freedom to choose, even if those choices are bad. I guess marijuana is in the category of where choice should never be allowed, since there are so many "concerned" scientists looking out for us. Yeah ... let's bitch about the nanny state some more.

    Who said you had no freedom to choose? The only complaints marijuana has gotten on a science site are the made-up nonsense about medical benefits. Those lack any evidence basis. Is scientific truth 'torches and pitchforks'? Not at all.

    Smoke 'em if you got 'em - but advocates need to stop pretending they are any better than cigarettes or that they need it for a 'condition'. They want to get stoned and have no stigma. Well, I'd like to smoke a cigar after a steak in California but I can't do that either. Fair is fair.
    The thing with alcohol and prescription drugs is that there are mountains of evidence, studies, and cultural paradigms about the malignant effects of these substances. We all know these things can be “bad” for us. Yes of course drinking and partying is glamorized to a certain degree, especially in the age group discussed in this study, but people in that age group have already been exposed to the dangers of alcohol and drug abuse through school, family, movies, TV, and books. The difference with pot is that we have created this strange cultural safety net to help us avoid a substantial discussion about the potential dangers of marijuana use. We are constantly touting the absence of any incidences of marijuana overdose, we say its natural, grown from the earth, not manufactured, and we look at its medicinal properties as a good excuse to legalize, when in most cases people who really need it for medical purposes have no trouble getting it. By giving marijuana this reputation we are basically saying “hey, go for it, we’ve looked into this stuff and it’s OK”, but we really haven’t given people an accurate assessment. It’s not just about the physical damage, but the emotional and mental toll that begins to rack up as marijuana use increases. If it was like alcohol and other drugs we would not have such a gut reaction when a negative fact about pot use is put forth, instead people would gain a clearer picture and those who still want to use would go right ahead, just like people do with alcohol and other drugs. Now, I’m no scientist nor am I a political strategist so I cannot really discuss the validity or intentions behind this study, I simply believe that a lot of marijuana users have so much invested in this idea that weed is “safe” and consequence free, that any crack in this venire, any doubt, can be a little frightening, and their constant attempts to put down naysayers is a great disservice to future generations.

    for Science 2.0 to not know this study was funded by anti-drug groups is embarassing...

    morons believe anything, 100 years of lies, what's one more...

    from 0 states to half the country, from low 20% approval to almost 70%, study those numbers, lol

    The problem with your logic is this; everything is funded by someone. So your conspiracy tale means that Democrats can't trust any science done during the Bush administration, Republicans can't trust any science done now, and that aspirin does not work because the studies that got aspirin approved were done by pro-aspirin groups.

    The funding source is not an issue outside the fringes - attack the methodology, sure, but claiming that these researchers are unethical cheats (would you claim that if the same methodology resulted in pro-marijuana papers? Plenty of those have been written as well) because you are part of the 1 percent and don't take money from anyone else and remain intellectually pure is simple first-world elitism.