Does Smoking Marijuana Kill Brain Cells?

Does Smoking Weed Actually Destroy Brain Cells?

You might have heard about the rumor that smoking weed can kill your brain cells. This rumor has been circulating in the cannabis community for quite some time now, causing many people to fear cannabis use, even for medical purposes. Cannabis users are some of the most intelligent people around, and many of them can separate facts from rumors.

While it’s only natural to want to find out which part of the brain is affected by weed, and if there is actually a study that proves that marijuana kills brain cells, the truth is, there’s not one scientific study that can prove this rumor. There are no studies that suggest smoking weed can “kill” your brain cells.

Now that’s out the way, let’s dive into another question, one that has an entirely different answer: Does weed make you stupid?
marijuna doesn't kill
Figure 1. 

Can Weed Make You Stupid?

The idea that weed makes you stupid likely originates from observation of the acute effects of large doses of pot smoke.  Large doses can cause extreme sedation and couchlock.  It can cause perceptual disturbances and make you slur your words.  When viewing someone under the effects of extreme intoxication, it can certainly look like they have gotten really dumb.  They may lose coordination and begin stumbling or experience ataxia.  This is the result of the way cannabis affects cannabinoid receptors throughout the nervous system.  Cannabis plants contain cannabinoids, a chemical substance that can bind to the nervous system. This substance affects several functions such as movement, pain perception, and anxiety levels. When cannabinoids enter the nervous system, it causes many symptoms attributed to the behaviors of someone with a low IQ. Symptoms such as high pain tolerance, sedation, and movement inhibition may make it seem like the intoxicated individual has less than desirable mental capacity. The anticholinergic effect is notorious for causing lapses in memory. While the symptoms may appear inherent to the individual, they are only temporary and are not the result of damaged brain cells.
marijuana stimulates brain
Figure 2. 

The Studies

Study Location Details Do Weed Kill Brain Cells? Can it be ruled out that weed may lower IQ?
1. Chronic cannabis users exhibit a neuropsychological decline beginning from childhood to midlife. Dunedin, New Zealand (2012), information compiled by Duke University Adolescent-onset use associated with slight cognitive deficit NO NO
2. The effects of teenage marijuana use on intelligence: Results from two cohort studies. The University of Southern California and other universities (2016) Twin study shows a decline of about 4 IQ points in users NO NO
3. Evaluating the relationship between cannabis use and IQ in youths and young adults with a high clinical risk of psychosis. Harvard, Yale and other universities (2015) Users at high risk of psychosis showed higher IQ when the use of cannabis starts at later ages NO No

Figure 3.

Can Smoking Marijuana Kill Your Brain Cells?

Study #1 Chronic cannabis users exhibit a neuropsychological decline beginning from childhood to midlife.

The first study was done in Dunedin, New Zealand.  They followed about 1000 people from adolescence to age 38.  They found an 8 IQ point reduction in those who were heavy smokers of cannabis from adolescence through to middle age.  However, only 3.8 percent of people fit the criteria of heavy smokers through to middle age. It is also possible that the fall in IQ points is better explained by socioeconomic factors rather than the effects of cannabis.  At the same time, heavy smokers should take this information into account, especially those who began in childhood. The use of psychoactive THC is never recommended before the age of 18, and many experts caution about use even before the age of 21.  Using psychoactive marijuana in childhood is also associated with an increase in the prevalence of psychotic disorders in adulthood.

This study provides no evidence that weed can cause brain cells to die. It cannot be ruled out that weed may lower IQ.

Study #2 The effects of teenage marijuana use on intelligence: Results from two cohort studies.

This study was done using twins and published by the University of Southern California in cooperation with other universities in 2016.  Twin studies attempt to weed out the effects of environment versus genetics. A decline of about 4 IQ points was found in marijuana users compared to non-users.  Also, a decline in IQ was found over time in both groups. However, this decline from high school age into adulthood has been observed in the general population and is generally explainable by the fact that after high school people’s interests become less academic as some go to college and others discontinue schooling.  Also, the effects of social factors are not weeded out in this study, since those who admit to heavy illicit use tend to be of a lower socioeconomic status. Those with better jobs or schooling tend not to use as they can expect to need to be clean for drug tests in the course of employment. They must also be sober for school and work, unlike those who are unemployed.  This study provides no evidence that weed causes brain cell damage. It cannot be ruled out that weed may lower IQ.

Study #3 Evaluating the relationship between cannabis use and IQ in youths and young adults with a high clinical risk of psychosis.

The last study, published in 2015, was done to find out if marijuana use improves cognition in those with psychosis and at a high risk of psychosis.  The study found no difference in IQ between weed smokers and non-smokers. However, it found a higher IQ in those with a high risk of psychosis who started smoking weed at later ages.  This suggests that components of marijuana such as THC and the other cannabinoids may have the ability to provide some neuroprotective effects, as has also been observed in other studies.

Figure 4.

This study, much like the two above, shows no evidence that weed has qualities that can kill brain cells. It cannot be ruled out that weed may improve IQ in those at high risk of psychosis.  As for the question: ‘Does smoking weed cause brain damage?’, it is unlikely to be the case, having looked at the evidence from these studies.


Marijuana also has effects on the immune system. The anti-inflammatory benefits that comes with marijuana use, especially the non-psychoactive preparations used every day for health reasons, also has the ability to protect neurons and the myelin that coats them. The myelin is a protective covering that can sometimes be attacked by the body’s immune system. Studies suggest weed is not bad for the brain won’t make you dumb. Some studies even show that, due to its neuroprotective effect, weed can allow your brain to grow, making you slightly smarter. It’s also been proven that weed can help in neurogenesis – the growth of nervous tissues and new brain synapses.

This article about Medical Marijuana was published on and updated on October 27, 2022 . Medical facts in this article was checked and article was medically reviewed by our . Author of this checked article is
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