Does Consuming Cannabis Make You Stupid?

byMarcus Clarke3 minutes

No doubt, you’ve likely heard this question before: Does marijuana make you dumb?

Cannabis has proven to have high therapeutic value for everything from PTSD and depression to skin conditions, digestive issues and back pain. But when it comes to the common perception of marijuana turning consumers into bumbling fools who can’t focus on anything for more than a few seconds, studies examining whether this is true are few and far between.

That said, a new study published in European Neuropsychopharmacology at the end of 2018 looked at MRI scans of the brains of cannabis consumers and non-consumers. The study’s researchers concluded that the MRIs showed practically no difference between the two groups.

Cannabis & the Brain

The marijuana plant contains more than 100 different cannabinoids. These cannabinoids—for example, tetrahydrocannabinol (THC) and cannabidiol (CBD)—interact with the body’s endocannabinoid system (ECS). The ECS is a system of receptors found nearly anywhere in the body, including in the brain. The ECS influences different processes in the body such as:

  • Mood
  • Pain perception
  • Hunger

One way marijuana—THC in particular—can influence the brain is by stimulating the production of dopamine, the feel-good chemical. Other effects include potential interference with learning and performance-related tasks; this can happen when cannabis alters the functioning of the orbitofrontal cortex, an area that controls memories and focus.

What the Research Says About Marijuana Affecting Brain Function

Up until recently, most research indicated that long-term, chronic marijuana use may adversely affect cannabis consumers. This seemed especially true for adolescents, whose brain networks involved in cognition and functioning are still developing. In one study where adolescents consuming cannabis were observed for 18 months, it was found that cannabis showed adverse effects on:

  • Cognitive development
  • IQ
  • Executive functioning

This may be due to cannabis’s interaction with the part of the brain that controls metabolism—a lower metabolism may impair decision-making and cognitive skills.


The connection between marijuana and a perceived decline in brain function can also be attributed to the fact that regular cannabis consumers—especially those younger in age—have reported higher levels of impulsivity as a result of cannabis altering the brain’s white matter microstructure. White matter is critical brain tissue, which houses nerve fibres that help connect the signals between nerves. This is what allows the brain to send messages to the rest of the body.

In another study, adolescent marijuana consumers showed a decline in crystallized intelligence, which is defined as the ability to access information from long-term memory to use skills, knowledge and experiences. Though they noted this decline, the study’s authors couldn’t make a definitive link between the frequency of cannabis use and changes in the adolescents’ IQ.

The authors admitted that declines in IQ observed in cannabis consumers could be attributed to genetic and other causes. Some of these causes, such as socioeconomic factors, may also account for a greater likelihood of adolescents becoming chronic cannabis consumers.

Since these types of studies are self-reported, it’s possible the results are flawed as subjects don’t always correctly remember past incidents or may not be telling the truth.

The Latest Research on Marijuana & Intelligence

Cortical surface morphology. This is the key term to grasp when it comes to understanding that latest European Neuropsychopharmacology study. The cortical surface—the surface of the cerebral cortex—is measured in:

  • Thickness
  • Surface area
  • Gyrification—the process of forming the characteristic folds of the cerebral cortex

Observed in MRI scans, cortical surface morphology comprises changes in the thickness, surface area and folds of the brain’s grey matter. By monitoring area-specific changes in these cerebral cortex areas while marijuana was being consumed, the study was able to examine the differences in development between cannabis consumers and non-consumers.

The good news is that results showed cortical morphology wasn’t directly associated with cannabis consumption, dependence or even the age when consumption began in regular consumers of the plant.

Additionally, functional and cognitive decline associated with marijuana use wasn’t necessarily permanent, and could depend on the duration and degree to which cannabis was consumed.

So, if you’re concerned about your marijuana use affecting your brain, take a little vacation away from the plant and see how you feel. If you find a break from cannabis was beneficial for you, consider taking time off from marijuana at regular intervals. If not, by all means, carry on.

Although there’s a lot more room for further research on the topic, we’re happy to bust the popular myth that marijuana consumption alone doesn’t make you dumb.

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