In the US, marijuana is currently the most commonly abused illicit drug. Over 26 million Americans smoked marijuana at least one time in 2008. There are sixteen states currently with medical marijuana programs.
Forty years ago, there were reports claiming that brain damage was caused by smoking marijuana. There were descriptions of marijuana smokers as lazy, apathetic, dull, delusional, irrational, and unproductive, which then gave reason for people to assume smoking marijuana resulted in brain damage.
As modern brain imaging was invented, such as CAT scans, no evidence of brain damage was seen in heavy chronic marijuana smokers. At Tulane Medical School in the 1970′s, animal studies were accomplished looking at massive doses of THC. Massive in these studies was 100 times the psychoactive doses in humans. The first set of studies showed significant EEG brain changes with implanted electrodes in monkeys. These changes, however, switched back to normal within one hour of drug administration.
Additional testing with the monkeys was not conclusive. On autopsy, however, there appeared to be some damage to the monkey’s hippocampus. In humans, this area is associated with intellectual function. The assumption then was that smoking marijuana by humans resulted in brain damage.
Some years after the Tulane results, the National Center for Toxicological Research repeated the Tulane study with significantly more animals. There were 4 groups containing sixty five monkeys: 1) High dose THC inhaling 2) Low dose THC inhaling 3) Placebo 4) No inhalation at all. No brain abnormalities were seen in any of the groups.
Based on previous scientific evidence, marijuana induced brain damage could not really be proven. That could be changing. There was a new study in late 2010 that showed potential for marijuana smoking to lower cognitive function.
At a recent presentation at the Society for Neuroscience, Dr. Staci Gruber discusses a small participant study where pot was smoked before 16 years of age. The participants performed statistically worse on cognitive tests than both non-smokers and those who became chronic smokers in later years.
A larger study will need to be done, as there could be some validity regarding an immature nervous system being affected when marijuana smoking is started early with potential for long term vulnerability.
Author: Lawrence Greene, MDThis author has published 19 articles so far. More info about the author is coming soon.