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Does Marijuana Kill Brain Cells?

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?

Dear Head-scratcher,

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.

Sincerely,
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 cannabis kill brain cells?

Whether cannabis, or marijuana, kills brain cells remains unknown, and current research studies have yielded conflicting results.

Keep reading to learn more about what current studies have to say about marijuana’s short- and long-term effects on the brain.

Share on Pinterest Marijuana may affect a person’s appetite, pain regulation, and mood.

Please note that the studies covered in this article mainly consider the effects of tetrahydrocannabinol (THC) on the brain. THC is the psychoactive compound in marijuana, or cannabis, that creates the ‘high’ effect. THC is just one of over 100 cannabinoids found in marijuana.

The body naturally produces endocannabinoids, which are similar to cannabinoids. Both cannabinoids, such as THC, and these natural endocannabinoids, bind to the same receptors in the brain.

Researchers have identified two types of these receptors:

  • CB1 receptors located in the central nervous system
  • CB2 receptors, which develop in the peripheral nervous system

When endocannabinoids bind to CB1 and CB2 receptors, they affect the following body functions:

  • appetite and metabolism
  • pain regulation
  • learning
  • memory
  • mood
  • sleep
  • cardiovascular functions
  • reproductive functions
  • immune system functions
  • muscle and bone formation
  • coordination and motor control
  • reward and addiction behaviors

Cannabinoids, such as THC, and naturally occurring endocannabinoids may have significant effects on brain function and development. This is because regions of the brain that control memory, learning, motor control, and sensory perception contain high concentrations of CB1 receptors.

Current research on this topic has yielded conflicting results. Some studies suggest that THC has potentially permanent neurotoxic effects that impair people’s verbal learning, memory, and focus. Other studies indicate the opposite.

In one 2017 animal study, researchers compared differences in working memory between adult rats exposed to a synthetic cannabinoid and those exposed to glucose during adolescence.

The researchers found that the rats they exposed to cannabinoids had a significantly better working memory in adulthood than the control rats.

In another 2018 animal study, researchers found that exposure to THC induced brain tissue growth and improved learning and memory function in rats.

In a 2016 study, researchers assessed the cognitive function of 3,385 people aged 18–30 by looking at the data from the 25-year-long Coronary Artery Risk Development in Young Adults (CARDIA) Study that began in 1986. At year 25, 84% of these participants reported previous marijuana use, but only 9% reported using marijuana into middle age.

After adjusting for demographic factors, psychiatric conditions, and other drug use, the researchers found long-term exposure to marijuana was associated with impaired verbal memory.

However, they found no evidence to suggest an association between marijuana use and cognitive processing or executive function.

Whether marijuana kills brain cells remains unknown, and current research studies have yielded conflicting results. Read to learn more.