Does Marijuana Kill Brain Cells?

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July 31, 2014 - By Malik Burnett, MD

Dr. Malik Burnett, policy manager for the Drug Policy Alliance in Washington, D.C., is a former surgeon and physician advocate. He also served as executive director of a medical marijuana nonprofit organization.

 


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 the marijuana also kills brain cells?

Sincerely,
Head-scratcher

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.

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