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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This site is not designed to and does not provide medical advice, professional diagnosis, opinion, treatment or services to you or to any other individual. Through this site and linkages to other sites, the Drug Policy Alliance provides general information for educational purposes only. The information provided in this site, or through linkages to other sites, is not medical advice and is not a substitute for medical or professional care. The Drug Policy Alliance is not liable or responsible for any advice or information you obtain through this site.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
Myths About Marijuana
The following mythology concerning marijuana is taken from the website of the National Organization for the Reform of Marijuana Laws (NORML, http://www.norml.org). References for these texts may be found there.
Myth: Marijuana Leads to Harder Drugs
There is no scientific evidence for the theory that marijuana is a “gateway” drug. The cannabis-using cultures in Asia, the Middle East, Africa and Latin America show no propensity for other drugs. The gateway theory took hold in the sixties, when marijuana became the leading new recreational drug. It was refuted by events in the eighties, when cocaine abuse exploded at the same time marijuana use declined. As we have seen, there is evidence that cannabis may substitute for alcohol and other “hard” drugs. A recent survey by Dr. Patricia Morgan of the University of California at Berekeley found that a significant number of pot smokers and dealers switched to methamphetamine “ice” when Hawaii’s marijuana eradication program created a shortage of pot. Dr. Morgan noted a similar phenomenon in California, where cocaine use soared in the wake of the CAMP helicopter eradication campaign. The one way in which marijuana does lead to other drugs is through its illegality: persons who deal in marijuana are likely to deal in other illicit drugs as well.
Myth: Pot Kills Brain Cells
Government experts now admit that pot doesn’t kill brain cells. This myth came from a handful of animal experiments in which structural changes (not actual cell death, as is often alleged) were observed in brain cells of animals exposed to high doses of pot. Many critics still cite the notorious monkey studies of Dr. Robert G. Heath, which purported to find brain damage in three monkeys that had been heavily dosed with cannabis. This work was never replicated and has since been discredited by a pair of better controlled, much larger monkey studies, one by Dr. William Slikker of the National Center for Toxicological Research and the other by Charles Rebert and Gordon Pryor of SRI International. Neither found any evidence of physical alteration in the brains of monkeys exposed to daily doses of pot for up to a year. Human studies of heavy users in Jamaica and Costa Rica found no evidence of abnormalities in brain physiology. Even though there is no evidence that pot causes permanent brain damage, users should be aware that persistent deficits in short-term memory have been noted in chronic, heavy marijuana smokers after 6 to 12 weeks of abstinence. It is worth noting that other drugs, including alcohol, are known to cause brain damage.
Myth: Prohibition Reduces the Harmfulness of Pot Smoking
Whatever the risks of pot smoking, the current laws make matters worse in several respects: (1) Paraphernalia laws have impeded the development and marketing of water pipes and other, more advanced technology that could significantly reduce the harmfulness of marijuana smoke. (2) Prohibition encourages the sale of pot that has been contaminated or adulterated by insecticides, Paraquat, etc., or mixed with other drugs such as PCP, crack and heroin. (3) By raising the price of marijuana, prohibition makes it uneconomical to consume marijuana orally, the best way to avoid smoke exposure altogether; this is because eating typically requires two or three times as much marijuana as smoking.
Myth: Pot is Ten Times More Potent and Dangerous Now Than in the Sixties
The notion that pot has increased dramatically in potency is a DEA myth based on biased government data, as shown in a recent NORML report by Dr. John Morgan. Samples of pot from the early ‘70s came from stale, low-potency Mexican “kilobricks” left in police lockers, whose potency had deteriorated to sub-smokable levels of less than 0.5%. These were compared to later samples of decent-quality domestic marijuana, making it appear that potency had skyrocketed. A careful examination of the government’s data show that average marijuana potency increased modestly by a factor of two or so during the seventies, and has been more or less constant ever since. In fact, there is nothing new about high-potency pot. During the sixties, it was available in premium varieties such as Acapulco Gold, Panama Red, etc. , as well as in the form of hashish and hash oil, which were every bit as strong as today’s sinsemilla, but were ignored in government potency statistics. While the average potency of domestic pot did increase with the development of sinsemilla in the seventies, the range of potencies available has remained virtually unchanged since the last century, when extremely potent tonics were sold over the counter in pharmacies. In Holland, high-powered hashish and sinsemilla are currently sold in coffee shops with no evident problems. Contrary to popular myth, greater potency is not necessarily more dangerous, due to the fact that users tend to adjust (or “self-titrate”) their dose according to potency. Thus, good quality sinsemilla is actually healthier for the lungs because it reduces the amount of smoke one needs to inhale to get high.Myths About Marijuana The following mythology concerning marijuana is taken from the website of the National Organization for the Reform of Marijuana Laws (NORML, http://www.norml.org). ]]>