Does Smoking Marijuana Kill Brain Cells?

How Many Brain Cells Does Smoking Weed Kill?

Smoking too much weed killing brain cells is a rumor many people have heard and is widely feared among the cannabis community.  Cannabis users are actually some of the most intelligent people around and are greatly protective of their intellect.  They want to know what part of the brain does smoking weed effect and if there is a ‘marijuana kills brain cells study’?  There is not.  There are no studies that suggest smoking weed will kill brain cells.  However, Does weed make you stupid? is another question with a different answer.

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.  Cannabinoids in cannabis bind to CB1 receptors in the nervous system. This affects pain perception, movement, anxiety levels, and other functions.  It can reduce pain, cause sedation, and inhibit movement, resulting in some of the symptoms that may look like a lower IQ.  The anticholinergic effect is notorious for causing lapses in memory.  However, this effect is temporary and is not the result of damage to brain cells.
marijuana stimulates brain
Figure 2. 

The Studies

Study Location Details Do Weed Likely Kill Brain Cells? Can it be ruled out that weed may lower IQ?
1. Persistent cannabis users show neuropsychological decline from childhood to midlife Dunedin, New Zealand (2012), information compiled by Duke University Adolescent-onset use associated with slight cognitive deficit NO NO
2. Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin 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 youth and young adults at clinical high 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 Marijuana Kill Your Brain Cells?

Study #1 Persistent cannabis users show neuropsychological decline 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 a decline of about 8 IQ points 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 kills brain cells.  It cannot be ruled out that weed may lower IQ.

Study #2 Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin 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 kills brain cells. It cannot be ruled out that weed may lower IQ.

Study #3 Evaluating the relationship between cannabis use and IQ in youth and young adults at clinical high 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 like THC and other cannabinoids may provide some neuroprotective effects, as has also been observed in other studies.

Figure 4.

This study provides no evidence that weed kills 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 effect that happens when you use marijuana, especially non-psychoactive preparations used every day for health reasons, can also protect neurons and the myelin which coats the neuron.  This protective membrane can sometimes come under attack by the immune system. Studies suggest weed is not bad for the brain won’t make you dumb.  Some research suggests weed can make your brain grow slightly smarter through its neuroprotective effect. Weed has also been shown to cause neurogenesis, the growth of new brain synapses.

This article about Medical Marijuana was published on and updated on May 25, 2020 . Medical facts in this article was checked and article was medically reviewed by our . Author of this checked article is
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shannon hays said:

I do believe this article is very true. I suffer from chronic migranes,depression, and stomach issues from having spinal meningitis in 1999 while 7 months pregnant. When i smoke weed it stops the migraine, eases my nausea and helps me relax until my body recovers from the incodent. As with my stomach issues, i rarely have a appetite to eat and since i am borderline diabetic and having had gastric-bypass i have to eat several small meals (snacks) every day, and weed gives me the apetite to eat and lets me keep my food down. When i eat if i dont smoke i get extremely nauseas, dizzy, and sometimes black out from throwing up. Also my depression seems better to me when I smoke. I am a creativer person (artist) and i put my depressed feelings into being creative with my poetry, and things i hand make. It also helps me control my meditation alot better so therefore i am able to control my heart beat, breathing and focus much better. I would love to see more articles like this such as how it cures different conditions, how it is used etc…
thank you for your time and May Gob Bless You All.. Keep on smoking!!!!

shannon hays said:

Also there needs to be a way to share these articles on social media like facebook and twitter. Any ideas on how i can share this on facebook??

Coloradopolarbear said:

With so much obvious corruption in government & facebook, how do you know this article wasn’t written by a marijuana smoking government “official” From marijuana users, I know this is not true.

dawn said:

copy and paste url into facebook message and post…

Garrett Litt said:

This article is written at a fifth-grade level. Good work representing the cannabis community :/

sandiswa brett said:

it is just a rumour because weed does not kill brain cells and it has been proven to the scientifically