A recent study published in the American Journal of Psychiatry demonstrated that people who use cannabis chronically and long term from age 18 through mid-life have cognitive deficits that are more significant than even those seen in long term alcohol abuse. Of note is that another study demonstrated that those who began regular cannabis use in adolescence experienced an average decrease in IQ of 6 points. The same cognitive decline was not observed in people who used it either infrequently or recreationally.
It should also be stated that there have been mixed results on studies examining the brain structure itself in those who use cannabis chronically and long term. Some studies demonstrate reduced volume of brain regions involved in executive functions such as memory, learning, and impulse control while other studies do not.
The takeaway message is that there seems to be a correlation between the chronicity of use and the length of time of cannabis ingestion/inhalation and cognitive decline. If started in adolescence, the more frequently it is used and the longer it is used seems to impair cognition enough to lower IQ by the time mid-life is reached. One of the largest groups using cannabis regularly are the Baby Boomers (those born between 1946 and 1964). This group as a whole used cannabis as young adults and now are using it again in mid-life.
It would appear that it would be of benefit to decrease the amount and frequency of cannabis ingestion from late teens to early adults. More studies need to be done to establish a definitive pattern before we say that without exception, one will be less intelligent by the time they reach mid-life if they started using cannabis regularly beginning in their teens. I do believe a case could be made for abstention or at least moderation to prevent this from happening.
As with many issues in the field of medicine today, one must also examine how and by whom the research was funded now that politics are playing a larger role than ever in scientific studies. In many cases, we can sadly no longer accept every piece of research as being unbiased. Given studies need funding (i.e. need money!), those with the most financial resources can influence the study itself and/or the take home message. Mark Twain noted that there are lies, damned lies, and statistics. In other words, statistics can be “massaged” to give the appearance of a desired result to satisfy a corporate entity or political group. So as health care providers and even patients, we must not only be up to date on emerging new research, but we also must make sure we know who is behind the studies and if there is a biased conflict of interest skewing the conclusions from that research.
