Does Marijuana Kill Brain Cells?

There is unquestionable proof that alcohol kills brain cells. The substance, which has been completely legal throughout American history barring a disastrous 14-year prohibition experiment in the early 20th century, results in the body’s digestive process creating acetaldehyde metabolites and other reactive oxygen species that are toxic to cells in the body, including those in the brain.
A college friend of mine once charmingly joked about the ‘buffalo theory’ whereby alcohol only kills brain cells you don’t need! In any case, those who speak against marijuana try to claim that weed does the same thing as alcohol. This is why the ‘stoner stereotype’ myth persists in some circles. To be clear, it IS fiction and based almost entirely on a single flawed study.

The Dunedin Experiment

It is a study by Duke University, published in the Proceedings of the National Academy of Sciences (PNAS) in 2012 which is responsible for the persistent myth that marijuana lowers IQ. The study was led by Madeline Meier and involved analyzing over 1,000 children born in the town of Dunedin, New Zealand.
The headline results of the study have been used by anti-marijuana lobbyists since they were published. In a 2014 edition of NBC’s Meet the Press, Ruth Marcus of the Washington Post said that while states should experiment, she did not agree with allowing full legalization. The reason? A study from Dunedin! Marcus said the following about it: “We do not know the outcome except that the best evidence is that you lose, (if you use marijuana as a teenager regularly) eight IQ points.”
This is a damning statement, and while there is a grain of truth to it, like so many others, Marcus failed to see the wood for the trees.The children in the study were born in the 1970s and took an IQ test aged 13. A series of follow-up interviews took place, and the volunteers outlined whether they used alcohol, weed, or other drugs. Another set of IQ tests followed when the volunteers were 38 years old. Tests on regular marijuana users found that their IQ fell by eight points on average.
If you believe this is the irrefutable evidence you’ve been searching for, think again. There are a host of caveats that anti-cannabis activists either glossed over or ignored in their rush to condemn the herb. First and foremost, the IQ loss occurred in chronic users who were physically dependent on weed before reaching adulthood. Less than 4% of volunteers showed a precipitous reduction in their IQ, and they had all been using marijuana at least four days a week over a span of two decades.
This suggests that hopeless addiction to marijuana, coupled with decades of use, IS bad for the brain, but we already knew that! There is also the small matter of socioeconomic status which, probably contributed to the results. Sadly, the researchers did NOT investigate this avenue, which means we have no idea if other factors resulted in (a) the physical dependence on the drug, and (b) if a lack of education was a bigger factor in IQ loss than marijuana use.

The Realities of IQ

A study by Cassidy et al., published in the journal Learning and Individual Differences in 2016, found that undertaking ‘online relational skills’ training could boost IQ by an incredible 23 points on average, significantly more than the loss enduring by the Dunedin marijuana addicts. If such a rise is possible, it is a distinct possibility that the learning habits (or lack of) of these patients had as much to do with the drop in IQ as weed.
In 2013, Ole Rogeberg published a paper on the Dunedin study IQ loss in the Proceedings of the National Academy of Science. According to the Norwegian Economist, children from poorer households could lose ground on IQ tests over time because they were more likely to complete work that was less mentally demanding. He said “the methodology” of the Dunedin study “is flawed and the causal inference from the results premature.”
Meier claimed that, when her team looked into income, they still found an IQ drop tied to weed use. What she didn’t – or couldn’t – do, is outline the size of the IQ loss. As the Dunedin group was rather small, with a maximum of 124 marijuana users at any time, the authors of the study couldn’t realistically, or accurately, take socioeconomic factors into account.

Could Marijuana Use Help CREATE Brain Cells?

Another study, this time by Jackson et al., published in the Proceedings of the National Academy of Sciences in 2016, compared pairs of twins over a period of a decade. One of the twins smoked weed in each instance, while the other did not. Once environmental factors were considered, no measurable link between weed and a drop in IQ was found. While the marijuana using twins showed a drop of up to four IQ points, so did the non-using twins.
A study by Mokrysz et al., published in the Journal of Psychopharmacology in 2016, focused on 2,235 teenagers in Britain. Once again, the goal of the study was to check the links between cannabis use in adolescents and their IQ, along with their level of educational attainment. The study found no noticeable difference between teenagers that used marijuana and those who did not. Of course, we are NOT advocating weed use in adolescents, but it is important to recognize the flaws of the much-hyped Dunedin study.
An Italian study by Di Marzo and Shinjyo, published in Neurochemistry International in 2013, found that the CBC in cannabis boosts the availability and functionality of developing brain cells. As well as stimulating the growth of new brain cells and preserving the brain’s health, CBC could even protect you against depression and other cognitive disorders.

Final Thoughts on Whether Marijuana Kills Brain Cells

There is no question that excessive marijuana usage is akin to playing with fire as far as your brain is concerned. A 2006 study, led by Lambros Messinis and published in Neurology, found that long-term weed users became less adept at learning or remembering things. For the record, the study focused on 20 long-term users who smoked at least four joints a week for 15 years or more.
Their brains didn’t function as well as users who averaged the same amount of use over a period of seven years. In other words, those who become dependent on marijuana have to work harder to retain their mental acuity. However, it is a complete falsehood to suggest that weed kills an enormous amount of brain cells to the point where you become less intelligent. The few studies that reach this conclusion are inherently flawed because they fail to consider things such as socioeconomic factors which could also reduce IQ.
It is far more interesting to learn that marijuana could potentially improve brain health when used responsibly. Far from damaging brain cells, cannabis’ cannabinoids may help rebuild them! For the record, the process of brain cell creation is known as neurogenesis, and it happens throughout our lives. Perhaps cannabis is capable of stimulating neurogenesis? We hope further study will help provide a clearer answer.

Sources
http://www.pnas.org/content/early/2012/08/22/1206820109*
https://www.marijuanabreak.com/does-smoking-weed-kill-brain-cells
https://www.sciencedirect.com/science/article/pii/S1041608016300231*
http://www.pnas.org/content/early/2013/01/09/1215678110*
http://www.pnas.org/content/113/5/E500*
http://journals.sagepub.com/doi/abs/10.1177/0269881115622241*
https://www.sciencedirect.com/science/article/pii/S0197018613002106*
https://www.ncbi.nlm.nih.gov/pubmed/16534113*