Does Marijuana Kill Brain Cells?
I have heard that marijuana use can lead to lower IQ, but I have also seen marijuana use help children with seizure disorders. I know that alcohol kills brain cells, is it true that marijuana also kills brain cells?
Thanks for your question.
First, let’s take a moment to address the notion that marijuana use leads to lower IQ. This idea came from a research paper which looked at data from a longitudinal study done on 1000 people from Dunedin, New Zealand. The study followed subjects from age 13 to 38 and conducted IQ tests a both these ages. The findings revealed that people who were chronic users of marijuana, which are those that had a physical dependence to the drug, before the age of 18 had a drop in IQ of 8 points by the age of 38.
There are three important things to note about this study. First, the people who were shown to have a decline in IQ are significantly small – 38 out of 1000, or 3.8 percent. Second, these individuals were using significantly more marijuana (four days per week) than the average marijuana user. Finally, they were using more marijuana consistently for much longer (20 years) than the average marijuana user.
Moreover, follow up studies of this data have shown that differences in socioeconomic status may account for the differences in IQ found in the study, not to mention the discussion surrounding IQ as a valid measurement of brain function and intelligence which are beyond the scope of this response.
In terms of marijuana and its effects on brain cells, or neurons, there is little evidence to suggest that any of the active ingredients in the marijuana plant administered at doses appropriate for human consumption have neurotoxic effects.
This is in direct contrast to alcohol, where the body’s digestive process creates metabolites such as acetaldehyde and other “reactive oxygen species” which are toxic to the brain and other cells in the body. This is why you have a hangover, after drinking large quantities of alcohol.
The active ingredients in the marijuana plant, called phytocannabinoids, affect specific receptors within the body. In fact, the body produces its own set of cannabinoids called endocannabinoids and has an endocannabinoid system which regulates the activity of all cannabinoids in the body.
There are two types of receptors within the endocannabinoid system CB1 receptors and CB2 receptors. CB1 receptors are located primarily in the brain and nervous system, while CB2 receptors are located primarily in the immune system.
The fact that these receptors are located all over the body is part of the reason why marijuana has been found to be useful for so many different medical conditions.
Specifically in the case of seizures, there is preliminary research which shows that the cannabinoid, cannabidiol or CBD, raises the threshold for seizure activity within the brain making it overall more difficult to have seizures, and thus providing hope to many parents of children with intractable seizure disorders. There is also some preliminary research which show that other cannabinoids within the plant actually protect brain cells from damage associated with Alzheimer’s disease. However, much more research needs to be done in order to make definitive claims on the medical benefits.
The evidence at this point indicates that marijuana does more good than harm when it comes to its effects on the adult brain.
Malik Burnett, MD
Dr. Malik Burnett is a former surgeon and physician advocate. He also served as executive director of a medical marijuana nonprofit organization. Amanda Reiman, PhD, holds a doctorate in Social Welfare and teaches classes on drug policy at the University of California-Berkeley.
This infographic has more information on how the brain processes cannabis.
UPDATE: This piece was originally posted on July 31, 2014 and was updated to include the infographic.
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Dear Docs: I have heard that marijuana use can lead to lower IQ, but I have also seen marijuana use help children with seizure disorders. I know that alcohol kills brain cells, is it true that marijuana also kills brain cells? Sincerely, Head-scratcher See the full infographic
Does smoking weed kill brain cells?
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- Origins of the myth of marijuana killing brain cells
- An overview of the research
- Studies on cannabis use and brain activity
- How to consume cannabis the smart way
- Bottom line on weed and your brain
For more than a century, rumors have persisted about the supposed dangers of smoking marijuana. From the War on Drugs to cultural commentaries in film and media, smoking weed has often gotten a bad rap.
Here we’ll debunk the myths about smoking weed and dive into the research to discover whether cannabis use can kill brain cells.
Origins of the myth of marijuana killing brain cells
The age of prohibition in the twentieth century coincided with some wild misconceptions about smoking weed and its effects on consumers. The two most prominent contributors to ongoing misconceptions about marijuana harming the brain are Reefer Madness and the fried egg campaign.
Reefer Madness is a 1936 film that experienced a resurgence in the 1970s and depicted excessively violent events linked to marijuana use. The melodramatic scenes show young adult cannabis smokers descending into various forms of madness and hallucinations until the dire advisory flashes on the screen at the end, “TELL YOUR CHILDREN.”
Reefer Madness is a 1936 film that experienced a resurgence in the 1970s and depicted excessively violent events linked to marijuana use. Photo by: Gina Coleman/Weedmaps
The fried egg campaign is one element of Reagan-era programs like DARE (Drug Abuse Resistance Education) that sought to educate children in the 1980s about the potential dangers of drugs. To this end, Partnership for a Drug-Free America (PDFA) sponsored a scare-tactic public service announcement with the image of an egg being dropped into a sizzling frying pan. In the background, a man gravely warned, “This is your brain. This is your brain on drugs. Any questions?” The first fried egg ad ran in 1987 and it was revived as recently as 2016.
An overview of the research
Dr. Adie Rae, neuroscientist and scientific adviser to Weedmaps, made the distinction between infrequent cannabis use and regular cannabis use, which may have very different effects on the brain. The available research supports the notion that occasional cannabis use may have neuroprotective effects on the brain, whereas the effects of frequent cannabis use are less clear but could be negative.
Rae shared, “The only evidence I could find in the literature of neurotoxicity to brain cells is caused by synthetic cannabinoids (such as Spice and K2). Plant-based cannabinoids appear to do the opposite, at least in the short term.”
Studies on cannabis use and brain activity
Many of the cannabinoids in cannabis (especially CBD and CBG but THC as well) are actually neuroprotective, according to Rae. “That means they turn on healthy cellular processes like antioxidation, rather than stimulating the cellular processes that lead to cell death. Being neuroprotective is what makes cannabis and its derivatives attractive targets as therapies for degenerative brain disorders like Parkinson’s and Alzheimer’s,” she said.
One 2020 literature review published in Molecular Neurobiology indicated that THC and CBD could potentially be therapeutic for individuals with Parkinson’s and Alzheimer’s disease.
A study performed on mice published in 2018 in Neurobiology of Aging showed that a very low dose of injected THC may trigger a reversal of age-related cognitive impairments. The positive effects lasted seven weeks.
On the other hand, one study published in 2020 in the journal Addiction Biology showed that the total size of the hippocampus, which is important for memory and learning, continues to get smaller with more frequent cannabis use “Cannabis isn’t necessarily ‘killing’ brain cells, but there is clearly something that is not normal in the hippocampus of chronic cannabis users,” according to Rae.
While cannabis doesn’t ‘kill’ brain cells, chronic cannabis use diminishes the production of key proteins that serve as survival tools for brain cells. Photo by: Gina Coleman/Weedmaps
In addition, some frequent cannabis users have reduced gray matter volume in several regions across the brain. Rae cited a 2020 study published in the scientific journal Neuroreport that demonstrated these gray matter changes in heavy cannabis consumers. “Again, this doesn’t mean that cannabis is ‘killing’ these brain cells, but the areas are smaller than normal,” Rae said. “Further, chronic cannabis use diminishes the production of key proteins that serve as survival tools for brain cells.”
How to consume cannabis the smart way
Moderation is the best way to ensure that you can safely enjoy marijuana and possibly even derive some brain-protecting effects. Rather than consuming cannabis daily, consider reducing your consumption and setting aside your favorite strain as a treat rather than a habit.
Choosing low-THC strains that have fewer psychoactive properties may also be a smarter way to enjoy cannabis. Some popular low-THC strains include Ringo’s Gift, Harlequin, Cannatonic, Pennywise, ACDC, and Sour Tsunami.
Finally, experimenting with smoke-free cannabis consumption methods may be better for your brain (granted to potency is low) and will certainly be better for your lungs.
Bottom line on weed and your brain
While studies have shown negative effects on the brains of frequent cannabis consumers, lower doses of THC may be beneficial.
“Because the endocannabinoid system is so involved in all of our cognitive and homeostatic processes, it’s wise to use cannabis moderately and/or take regular breaks,” Rae said. She recommends at least 48 hours of abstinence at least once a month.
This advice, however, is for adult consumers, not those whose brains are still developing. “There are definitely developmental effects of cannabis on the developing brain, whether a person is in utero or in high school. The safest thing for brain health is to wait until the brain is fully developed, around age 22, before using cannabis,” said Rae.
It would seem that, when it comes to cannabis consumption and brain health, less truly is more.
Here we'll debunk the myths about smoking weed and dive into the research to discover whether cannabis use can kill brain cells.