Studies show potential harms of marijuana

Time and time again, I have heard people say that marijuana is not that bad for you. It is the most commonly-used prohibited drug in the United States, and an estimated 18.9 million people are lighting up (Science Daily, “Brain changes associated with casual marijuana use in young adults, study finds,” 04.15.2014). Users will justify this by saying it “isn’t as bad” as another drug or that marijuana does not affect academic performance. In the past, the drug has been associated with impairments with attention and motivations, but it has been suggested that these changes occur with long-term users.

However, new studies propose that marijuana may be linked to significant brain changes in both casual and long-term users, and the drug has also been linked to heart problems. For so long, it appears that the concern has been with long-term marijuana smokers and those who smoke high amounts of the drug. Researchers are investigating casual smokers, and the results leave one with many questions, including: Is marijuana as “safe” as we thought for casual use, and should we continue the push to legalize it?

In a recent study published in the Journal of Neuroscience, professors from Northwestern University teamed up with doctors from Massachusetts General Hospital and Harvard Medical School to investigate the brains of twenty casual marijuana users ages 18 to 25. They compared MRIs of the brain of casual smokers (those who reported smoking at least once per week) to non-smokers. The cannabis use was recorded for 90 days. The results showed that the nucleus accumbens, a brain structure that has been associated with anticipation and expectation of reward, was enlarged and altered in shape for the marijuana users. The amygdala, a brain structure associated with emotions and feelings, was also found with multiple abnormalities in the marijuana users who used it casually or regularly (Journal of Neuroscience, “Cannabis Use is Quantitatively Associated with Nucleus Accumbens and Amygdala Abnormalities in Young Adult Recreational Users,” 04.16.2014).

Dr. Hans Breiter, co-senior author of the study and a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, notes, however, that none of the users reported any problems with school, work, legal issues, parents or relationships, despite the structure changes.

Another doctor involved in this study, Dr. Staci Gruber, Director of the Cognitive and Clinical Neuroimaging Core at McLean Hospital in Boston and a professor of psychiatry at Harvard Medical School, who has been known for her numerous studies involving marijuana use and brain function, acknowledges that users do not have the problems listed by Dr. Breiter but suggests that follow-up with these patients and/or further investigation is necessary (CNN, “Casual marijuana use may damage your brain,” 04.16.2014).

The brain is still developing through a person’s late teenage years and even through her or his twenties. Dr. Gruber is concerned with possible developmental changes and suggests that age may play a role in the effect that marijuana has on certain structures. She openly states that results at this time don’t really say much but says that the next step would be to see how the structural differences relate to functional outcome.

So, what does this mean, and where do we go from here? We already knew that structural changes occurred with long-term marijuana use, and now we have just expanded these changes to those who use casually. However, we are not really sure what these structural changes mean. Because I learn about the nucleus accumbens in many classes and how this structure helps us recognize anticipation, I am curious to see if it prolongs or enhances feelings of thirst or desire.

However, at this time, no real conclusions are made about the use of marijuana. This is just the beginning in an large amount of studies that will need to be conducted in the near, as well as distant, future to make a definitive conclusion about how these structures are really affected qualitatively and not just quantitatively by marijuana use.

What most do not realize is that every year, we are making new discoveries about the brain and are redefining certain structures. Even this semester, I’ve figured out that I had previously learned about some structures incorrectly, and I had to learn the newfound functions of those structures. There are even identified structures and we have no idea what they do. That’s just the honest truth about neuroscience—it is constantly evolving and expanding. We are always learning new things about the brain and how it is affected in different ways.

So, we don’t know everything about how marijuana really affects the brain. The same is true for other drugs that are currently on the market. We know a lot, but not everything, and we make best guesses. In reality, drugs affect everyone differently, and with a lot of drug studies, confounding variables are present, which ultimately alter results.

This study is simply making a small wave during a time of discussion regarding the legalization of marijuana. While this study may bring up valid concerns, it does not provide a definitive reason to not legalize marijuana. Alcohol causes impairments while one is under the influence. It has been associated with negative long-term usage effects and yet it is still legal.  I think the real concern with legalization would be the concerns of safety and responsibility while under the influence of marijuana. While we may not know all the risks associated, understanding the lack of knowledge is something of which one should be aware before lighting up.


—Delaney Fischer ’15 is a neuroscience major.

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