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Alcohol vs. marijuana in the brain

Which drug is more dangerous?

Every year my students ask the same question about alcohol and marijuana: which is more dangerous to consume? In truth, this is a difficult question to answer because the two drugs have quite different and complex actions in the brain. Also, it's difficult to define what "more dangerous" really means with regard to the brain, particularly as compared to the well-known consequences of the consumption of alcohol on the body. Furthermore, the long term effects of both drugs are often quite different from their short term effects. Also, as I emphasized in my last blog about the relationship of marijuana smoking to psychosis, relative danger depends importantly upon specific genetic vulnerabilities inherited from our parents. Therefore, I find that answering this perennial question is often analogous to comparing the proverbial apples and oranges. Recently however some advances in the research on both drugs have provided some additional insight into a partial answer, at least from the standpoint of the brain.

I was recently honored by an invitation to give a TED talk on this topic area. The video is available here.

A recent publication in Proceedings of the National Academy of Sciences from the Scripps Research Institute in California investigated the effects of binge alcohol consumption upon the adolescent brain. Many recent studies have already demonstrated that adolescence is a time of increased vulnerability of the brain to chemical insults. Furthermore, to make this issue even more timely, binge alcohol consumption by teenagers is increasing. The neuroscientists at Scripps discovered that binge alcohol consumption is particularly injurious to a region of the brain called the hippocampus. The hippocampus plays a critical role in learning and memory. Within the hippocampus are a group of cells that continually produce new brain cells, called neurons, throughout our life. This process of cell renewal is called "neurogenesis;" whenever this process is impaired we have trouble forming new memories and we develop the symptoms of depression, to mention just two consequences.

The Scripps scientists discovered that eleven months of binge alcohol consumption that produced a blood alcohol level sufficient to be considered intoxicated decreased neurogenesis by more than fifty percent! Furthermore, the decrease in neurogenesis lasted for many weeks of abstinence. You might think that alcohol binging also caused more cells to die; actually, this did not happen. That old urban myth is simply not true. The only change observed was a decrease in the production of new neurons. The authors suggested that these changes might produce a long lasting vulnerability within the hippocampus that may well predispose these young adults to neurodegeneration later in life.

In contrast to the effects of alcohol, a series of publications during the past few years suggest that stimulating the brain's marijuana neurotransmitter system appears to have the exact opposite effects upon neurogenesis in the hippocampus of both young and old laboratory animals and humans, i.e. neurogenesis is increased by stimulation of our brain's marijuana receptors.

When we are elderly, our brain displays a dramatic decline in neurogenesis within the hippocampus. This decline may underlie age-associated memory impairments as well as depression. Research in my laboratory has demonstrated that stimulating the brain's marijuana receptors restores neurogenesis. Thus, later in life, marijuana might actually help your brain, rather than harm it.

Considered together, the results of these studies can teach us a lot about the role of our endogenous marijuana neurotransmitter system during our brain's ongoing process of repair and re-wiring as we mature. Binge alcohol consumption during the more vulnerable periods of our lives is clearly able to interfere with these critical neural processes and produce significant long-term negative consequences. In spite of many recent advances by laboratories around the world, much remains to be investigated regarding the effects of these two commonly consumed chemicals upon the brain. At least next year I'll have a better answer to my students' recurring question.

© Gary L.Wenk, Ph.D., author of Your Brain on Food (Oxford, 2010);

See also: Marijuana and Coffee are good for the brain.

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