Does Marijuana Decrease Brain Function?

College is a time when many students begin experimenting with many things, including alcohol and illegal drugs. One of the most popular and enduring of these is marijuana. Despite some of the world’s most prominent and successful figures, such as Morgan Freeman, Bill Gates, and Barack Obama admitting to using marijuana in the past or present, there is still a stigma associated with it that it makes people lazy or stupid. While the success of those previously mentioned seems to do away with that notion anecdotally, the scientific results have been mixed.


One study performed at Washington University reviewed MRI scans of the brains of 241 sets of twins, where some sets had both smoked marijuana, some had just one user, and some has neither as users. The results suggested that the portion of the brain that deals with emotions and rewards was shrinking in the subjects who were marijuana users. Another study performed by Dr. Tomas Paus looked at the MRI scans of around 1500 adolescent boys two times, at age 15 and at age 19. The results appeared to show a thinning of the outer layer of the brain in those who were marijuana users. Finally, a study performed in New Zealand that followed subjects from their birth until they were nearing 40 showed lower IQ scores in people who had smoked marijuana, and especially in those who were frequent users. The researchers also surveyed people with close relationships to the subjects and found that those who smoked marijuana were struggling more in everyday life. The most surprising result of this final study is that subjects who began using marijuana during adulthood appeared to be less effected than those who began during their teenage years. However, despite these studies pointing towards marijuana having negative effects of cognition and success, there is certainly the possibility of confounding variables or chance being the reason for these results.


Overall, while there is no definite link between marijuana and decreased cognitive function, these studies do all make the case that pot can hold people back from their full potential and interfere with the brain. The research on this subject will certainly continue, especially with more and more states legalizing or decriminalizing marijuana in some form.

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1 thought on “Does Marijuana Decrease Brain Function?

  1. Brett Alan Merritt

    I have been hearing about the effects of marijuana for so long. Different research and different people argue for both sides. Seeing that the usage rate is going up and many states are legalizing it, do you believe that weed should be legal nationwide?

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