Marijuana Studies Show Link Between Not Smoking Pot And Impaired Reasoning Skills

Marijuana Study

If you thought marijuana was safe, thing again, as a recent cannabis study examining the brains of marijuana smokers has brought to light that for individuals who don’t smoke pot, merely thinking about it leads to serious impairments in logical reasoning. This disturbing news was brought to my attention via an article about observed brain “abnormalities” in marijuana smokers that was posted to my Facebook wall several days ago. The article, titled “Harvard Scientists Studied the Brains of Pot Smokers and the Results Don’t Look Good,” appeared on, an alleged news website of which I was previously unaware.

Harvard Scientists Studied the Brains of Pot Smokers, and teh Results Don't Look Good

Published in April of 2014, the observational study (a publication of limited news value) references, was spearheaded by principle investigator Hans Breiter and several researchers from a few of America’s most renowned universities including Harvard University in Boston and Northwestern University in Chicago. In order to examine what have been referred to as the “effects” of casual marijuana use on the brain, researchers in the cannabis study used MRI scans to compare the brains of 20 casual marijuana smokers and 20 non-smokers from a single area and between the ages of 18 to 25 years (i.e. a small and not very representative sample when extrapolated to a large and diverse population).

Marijuana Plant from Effects of Marijuana on the Brain Blog Post

The marijuana study identified group differences in the grey-matter density, shape, and size of two limbic system structures. The limbic system is the brain’s center for emotion, motivation, and natural drives like sex or hunger. Specifically, the MRIs showed that the left nucleus accumbens and the amygdala appeared to have higher grey-matter densities (i.e. more stuff that’s composed of neuronal cell bodies, dendrites and myelinated as well as unmyelinated axons, glial cells, and capillaries) in the brains of individuals who smoked pot at least once a week, but most of whom reported smoking more than ten joints per week. The observed differences, which also include a difference in the shape of the left nucleus accumbens and right amygdala, as well as increased volume in the left nucleus accumbens, were more pronounced in subjects who reported getting high more frequently. The study mentions that based on questionnaires, the pot smoking individuals also consumed significantly more alcoholic beverages per week than participants in the control group. Furthermore, compared to no cigarette smokers in the control group, 8 out of the 20, or 40% of subjects in the marijuana group also reported smoking cigarettes (which do all sorts of weird things to the brain). Surprisingly, despite making claims to the very serious and worrying implications of their marijuana study’s findings, head researcher Hans and his fellow investigators failed to assess any behavioral or cognitive performance measures, which may have lent themselves to classifying the observed structural differences as either good, bad, or mostly irrelevant.

Under any normal circumstances, these relatively uninteresting and largely meaningless findings, with few, if any, apparent implications, would have made their way into the annals of Google Scholar history shortly after print. However, thanks in part to a Northwestern University press release titled “Casual marijuana use linked to brain abnormalities – First study to show effects of small time use; more ‘joints’ equal more damage” and its false pretenses at causal significance (something which is notably impossible to establish in an observational study), and partly due to the hopeless bullshit that principle investigator Hans fed the less than discriminating international media, this marijuana study blew up, and getting scooped up by every imbecile reporter and their mother, made it to the front lines of world news.

Since the final sentence of the cannabis study’s abstract states the following:


and because Hans is quoted saying this in the university’s press release:


it’s unsurprising that news outlets throughout the world, who are remarkably prone to the logical fallacy of mistaking correlation for causation (i.e. the causal fallacy), thus bastardizing research findings and misrepresenting facts in the process, took this story and spun it out of control. Being that this sort of shoddy reporting is a daily occurrence, I would normally not have batted an eye at the media’s error. However, because the topic of marijuana and its widespread, extensively studied, well-documented health benefits is near and dear to my heart, I want to point out and correct the unfounded assertions that a cannabis study found smoking marijuana to cause brain damage in young adults. Whether they aimed to derail the battle for cannabis freedom or simply to create a hype, these so-called reporters and the questionable researchers who spoon-fed them nonsense, should be sanctioned for spreading these fallacies. There is precedent for this.
Thou Shalt Not Commit Logical Fallacies like the False Cause Fallacy

Image via

So, what exactly did some of our most-trusted information sources report?

The Washington Post – “Even casually smoking marijuana can change your brain, study says

The Oregonian – “Casual pot use impacts brains of young adults, researchers find

Time – “Recreational Pot Use Harmful to Young People’s Brains

The Times of India – “Casual marijuana use too bad for young adults

Gizmodo, UK – “Even ‘Casual’ Marijuana Use Can Knacker Bits of Your Brain

Medical News Today – “‘Casual marijuana use changes the brain,’ researchers say

MSN NZ – “Cannabis use ‘alters brain regions’: study

Science Daily (a surprising perpetrator of bad science reporting) – “Brain changes associated with casual marijuana use in young adults, study finds

Forbes – “Even recreational marijuana may be linked to brain changes

…and one of my personal favorites – NBC’s piece titled “Marijuana Re-Shapes Brains of Users, Study Claims” in which the author, Bill Briggs, declares that:

Two neural regions key to emotions and motivation become misshapen or abnormally large after repeated pot smoking, scientists reported Tuesday.

Referencing what he believes to be actual scientific findings, Bill throws in the following statement along with a link to the video below:

No need for that iconic, anti-drug image from the ’80s — a piping-hot pan and a frying egg — to make the latest visual point.

No need indeed, because what any discerning individual can tell you is that Bill’s cretinous reasoning abilities, lack of basic scientific understanding, inability to check facts (a simple search of Google Scholar for key terms like “brain size + IQ” would have exposed him to the scientific community’s overwhelming consensus that larger brains are actually a good thing, rather than evidence of brain damage as he and the anti-marijuana media have been quick to label them), and utter disregard for what the rest of us refer to as “The Scientific Method,” place him in the same boat as the idiots who produced the anti-pot flicks he refers to. Sadly, the above anti-marijuana tirades from self-dubbed “science” reporters like Bill, are just a few of the uninformed headlines that blasted the world this April. Reaching far too many undiscriminating individuals who took their would-be laughable, if they weren’t so damaging, allegations as truth at face-value, these “news reports” attest to just how uninformed today’s media actually is.

Luckily, I, a lowly marijuana smoker suffering from brain enlargement, can sense bullshit when it unceremoniously slaps me in the face. Perhaps the abnormally dense structures in my brain’s emotional center have made me extra sensitive to shitty science reporting.

But, if marijuana smokers’ brains differ significantly from non-smoker brains (and differ more with increased consumption frequency), how can the media’s reasoning possibly be flawed?

Well, let’s start with a similar example from the global warming camp. Have a look at the graph pictured below.

Global Temperature versus Number of Pirates

Image via

As you can see, the past 200 years or so have been characterized by steadily rising global temperatures and coinciding decreases in world pirate numbers. It’s evident then, that a statistically significant inverse relationship exists between global warming and number of pirates. Thus, just as the correlation between smoking marijuana and brain structure differences is taken to mean that brain differences are the direct result of smoking marijuana, global warming as well as earthquakes, hurricanes, and other natural disasters, which can be attributed to climate change, must also be the direct result of decreasing pirate numbers since the 1800s.

Sure, but how do we know that decreasing pirate numbers aren’t the direct result of rising world temperatures rather than the other way around?

The answer is, we don’t, but like our fellow science reporter Bill and others like him, we don’t need to, because most people will never think so far as to actually ask that question. These same people, presumably avid readers of sources such as NBC, Time, and the Washington Post are probably also unlikely to consider that perhaps both the increase in global temperatures and the decrease in number of pirates were actually the result of something else entirely – like say the devil’s hell fire.

In fact, according to recent reports from the Roman Catholic Church, increasing secularism and declines in religiosity throughout the West have reportedly “opened the window” to black magic and Satanism, thus providing the devil with an open invitation to warm the earth with hell’s fire. In demonstrating this significant correlation between rising satanism and increasing global temperatures, the Catholic church has shown that rather than being the result of decreasing pirate numbers, global warming is actually the direct result of satanism. As a solution, the Catholic Church has established a new training program designed to increase exorcism and cast evil from possessed folk. If this program succeeds, consequent decreases in Satanic worship, will cause a cooling of the devil’s fire, thus resulting in global average decreases in earth’s temperature.

Fine, but what do global warming, pirates, religiosity, Satan, and the Catholic Church’s exorcism training programs have to do with the brain differences that one observational cannabis study attributed to marijuana?

Note the following:

1. The False Cause logical fallacy consists of presuming that a real or perceived relationship between variables indicates that one is the cause of the other.

2. Relationships of statistical significance do not imply causality.

3. Only experimental studies can establish causality.

4. This marijuana study was an observational study.

5. Observational studies cannot establish causal relationships (^only experimental studies can).

So, what all of these examples share in common is one very nasty and pervasive error in logical reasoning. That is, if we try even a little bit, we can easily identify statistically significant relationships between variables such as rising global temperatures and decreasing pirate numbers, or plummeting religiosity and increasing devil worship. By way of this same reasoning we are able to establish further relationships between the drop in religiosity and the drop in pirates, the rise in satanism and the rise in global warming, as well as the increase of marijuana use and the increase in structural brain differences. However, to conclude that marijuana use causes brain abnormalities just because the two appear to be related by proxy of occurring at the same time, would be the same as concluding that the rise in devil worship causes global warming or that a drop in religiosity is behind falling pirate numbers. Observational data does not make this leap of logic possible. Yet, confusing correlation or simultaneity with causality (i.e. assuming that just because two things like increasing global temperatures and decreasing pirate numbers are occurring at the same time, they exist in a cause and effect relationship with each other) seems to be an ever-pervasive flaw of both Hans’ MRI study and the media, who typically jump to sensational conclusions, that are unsupported by evidence.
Marijuana Smokers Smell Cannabis at Alpenglow Botanicals Dispensary in Breckenridge Colorado

But, how else (other than by marijuana turning brains into fried eggs) can the marijuana brain imaging study’s findings be explained?

The number of possible explanations for the structural brain differences identified in this neuroimaging study borders on the infinite. However, a simple literature review of some previous studies examining differences in the same brain regions can lend itself to a better understanding of why this group of marijuana smokers may have exhibited differences in their nucleus accumbens and amygdala.

For example, one marijuana study published in 2005 (an experimental one – i.e. a study capable of establishing causality) examining the effects of cannabinoids (compounds found in marijuana) on the hippocampus, another limbic system structure, and our center for learning, memory formation, and spatial coding, found evidence to suggest that cannabinoids promote hippocampal neurogenesis (i.e. the formation of new brain cells or enlargement of brain regions). Notably, although experimental studies are in fact capable of establishing causality and researchers in this study found a significant relationship between cannabinoids and neurogenesis, the investigators were still careful not to overstate their findings. In fact, rather than asserting that cannabinoids actually cause neurogenesis the researchers simply stated they promote it.

Their findings are significant because starting in our late twenties the hippocampus typically begins losing an average 1% of its volume per year. Since hippocampal atrophy (i.e. size decrease) is associated with all sorts of horrible functional impairments (google them if you dare), finding ways to trigger regional brain enlargement is critical to helping both the young adult and aging populations lead happy, healthy, long, and fruitful lives. Opposite to what the Northwestern University study would like us to believe, different studies investigating neurogenesis (i.e. brain enlargement), including this 2005 cannabis study and other non-cannabis studies view brain growth as a good thing. They also identify several ways by which individuals can grow new brain cells, including eating more blueberries, engaging in sexual intercourse, and exercise. So, one possible explanation for the findings of Hans’ brain imaging cannabis study is that marijuana is in fact involved in neurogenesis and the resulting observed increases in limbic system brain structures like the nucleus accumbens and amygdala.

Another possible explanation of the Northwestern marijuana study’s findings lies in neuroimaging research examining the brain differences between people of average creativity and those who show above average creativity. Notable subjects include Steve Jobs (a marijuana smoker), filmmaker George Lucas, mathematician and Fields Medalist William Thurston, the Pulitzer Prize-winning novelist Jane Smiley and Nobel laureates from the fields of chemistry, physics, and physiology or medicine. This line of research has demonstrated significant relationships between extremely creative people and similar brain structures (based on their reasoning in the marijuana brain imaging study, the folks at Northwestern, would likely extrapolate these findings to mean that creativity causes brain damage). Interestingly, many of the renowned creatives in the study, also suffered from some form of mood disorder (ranging from mild, to extreme and including ailments such as anxiety, depression, bi-polar disorder, and mild schizophrenic symptomatology). These creatives generally showed a family history of mental illness, and presumably as a means of coping with their emotional struggles, were more likely to engage in substance use. This research, suggests that rather than being “caused by marijuana,” larger limbic system structures are somehow related to increased creativity and that highly creative people are simply more likely to use substances such as marijuana to cope with the emotional instability that can often be observed among their cohort.

If you search Google Scholar for keywords such as “enlarged amygdala,” or “enlarged nucleus accumbens” you’ll come across other studies examining differences in the sizes of these two structures. Similar to the findings of the creativity studies, some of these studies have identified relationships between structure size (for both smaller and larger than average sizes) and mental illnesses including schizophrenia, depression and bi-polar disorder. These relationships provide further support for the hypothesis that rather than marijuana use causing changes in limbic system structures, people with enlarged limbic structures may just be more likely to consume marijuana, drink alcohol and smoke cigarettes as a result of pre-existing underlying differences in the ways their brains operate.

Following the pattern of reasoning used in the Northwestern marijuana study’s assertions and based on all of the above research findings (along with more like them) — which if Hans had completed a proper literature review he would certainly have come across — if we are to believe what Hans and his proponents so vehemently suggest, then marijuana must be the cause behind not only larger brains, but also creativity, anxiety, depression, bi-polar disorder, etc. If that were the case, however, simply adding or removing marijuana to and from the mix, should address all of these problems. Since even a moron could tell you that is not the case (i.e. not smoking marijuana is not a cure for bi-polar disorder), I think we can safely assume that this cannabis study, its alleged anti-marijuana “findings,” and the researchers hailing their significant implications are all total bullshit.

How do we know that the brain differences observed in the marijuana study are bad and not good?

Based solely on this cannabis study’s findings, it’s impossible to determine whether the observed differences in brain structure size are good or bad. Other than identifying differences in drinking and cigarette smoking habits, the study did not investigate the behavioral or biological implications of the structural differences observed between the nucleus accumbens and amygdala of marijuana smokers and controls. However, a simple Google Scholar search for the terms “brain size + IQ” yields a slew of studies showing a positive relationship between brain size and intelligence. In addition, research examining the brains of London taxi drivers, who are required to memorize city maps in order to earn their hackney’s license, show them to possess an enlarged hippocampus, while imaging studies of symphony-orchestra musicians have shown them to have an unusually large Broca’s area, a brain region associated with language. Unsurprisingly, rather than being detrimental as Northwestern and Hans suggest, there is an overwhelming amount of evidence (including studies of evolutionary biology showing a correlation between brain size and the incredible advancement of the human species) to support the notion that a bigger brain is actually good for you.

Just as we cannot assume that the observed brain structure size differences (large for marijuana smokers and small for poor lowly non-smokers) Hans identified are the result of smoking marijuana, we also cannot simply jump to the conclusion that these differences are bad or even abnormal. In fact, even if they are the result of marijuana, considering the widespread health benefits of cannabinoids (like say neurogenesis and cancer cell destruction) and the abundant existence of cannabinoid receptors throughout nearly every part of the human body, it is simply wrong to conjecture that not consuming cannabinoids is the normal thing to do. Following this premise, we could just as well flip the news headlines around to say that people who don’t smoke marijuana have abnormally small brain structures when compared to those who do. Personally, having larger, more complex brain structures that possess more neurons and more neuronal connections sounds a whole lot better than having smaller ones (we’ve all heard of Alzheimer’s Disease). So in a sea of modern studies examining ways to prevent brain atrophy and build bigger brains, presenting larger brain structures as a negative seems rather abnormal. It’s possible that such false perceptions and an inability to employ reasoning are simply the result of smaller brain structures found in people who don’t smoke pot.

Either way, since this experimental study, published in October of 2005, demonstrated cannabinoids found in marijuana promote new brain cell growth, and studies have shown new brain cell growth to be associated with decreases in measures of dumbness, Bill, his reporter cronies, and the people at Northwestern University should probably light up a few joints before they write their next ‘scientific’ piece.

So, if you, like me, enjoy smoking some good old fashioned healing herb, worry not. You might just be a little more creative, a bit more anxious, or slightly more prone to getting sad than your non-smoking counterparts, and if Alzheimer’s Disease ever attacks your enlarged brain it will hopefully have grown so big (as a result of cannabinoid related neurogenesis and a preference for neuronal growth triggering blueberries as munchies), that, unlike small brained folks, you will never notice its detrimental effects.

*For a more technical assessment of this marijuana study’s various flaws, refer to Doctor Lior Pachter’s post titled “Does researching casual marijuana use cause brain abnormalities.” Doctor Pachter, the Raymond and Beverly Sackler professor of computational biology at UC Berkeley and professor of mathematics and molecular and cellular biology with a joint appointment in computer science, tears Hans Breiter (the study’s principle investigator) a new one and refers to his paper as quite possibly the worst he’s read this year (which considering his blog is devoted to ripping shitty research to shreds is saying a lot).
