Commentary by Dr. Patrick Slattery — The article below headlines a study showing that marijuana usage reduces verbal memory. When one considers stereotypical stoner speech mannerisms (think Sean Penn’s character from “Fast Times at Ridgemont High”), this should hardly come as a surprise.
Of course, if you read down the article, you see that the 25-year study of 5000 individuals actually found that marijuana was correlated to declines in all cognitive functions tested for. However, the article states that “after adjusting the results to take into account other factors such as depression or the use of other substances… the only statistically significant correlation that could be established was between the long-term use of marijuana and verbal memory.”
What does that mean? It means that pot smokers experienced cognitive declines, but that because pot smokers are more likely to be depressed or users of other drugs, it might not be the pot that is causing the decline but rather the depression or the other drugs.
Of course, this begs the question “does marijuana contribute to depression?” It may well, or it may be that depressed people are more likely to smoke it.
On the other hand, regarding drug abuse it is well established that marijuana use typically precedes that of most other drugs, with the possible exception of alcohol.
Even with all the equivocating about the contribution marijuana makes to the non-verbal cognitive declines seen in pot users, the article still concludes by remarking that “the general findings of the new study do correlate with previously available evidence that pot causes a decline in cognitive abilities and IQ scores.”
Marijuana is being legalized or decriminalized in numerous jurisdictions around the country, partly in response to perceptions that locking people up for long periods of time just for pot smoking is bad policy. Still, this study shows that the drug does indeed pose a major public health problem.
I would certainly agree that prosecuting people just for marijuana usage has clogged up the criminal justice system and made it more difficult to protect society from actual violent criminals, and also that locking up pot heads makes them less likely to reform and more likely to be a burden to society than simply ignoring their pot usage, let alone treating it as a public health problem.
This is why I think that decriminalization, as opposed to full legalization, is the appropriate path. It is important for society not to go along with the Zio media narrative that pot smoking is a harmless recreation, as this latest study makes clear.
And as for its medical uses, if it is an effective medicine that is all the more reason that it should not be used recreationally. What pharmaceutical is there that is harmless when used recreationally?
So it is a nuanced message, but one that makes sense. Let’s not lock up people for pot, but make it clear that getting high does have serious adverse consequences for your brain.
A study published in the journal JAMA Internal Medicine on February 1 maintains that a longstanding pot habit does not necessarily influence other cognitive or executive functions, be it processing speed, focusing or planning capabilities.
The effects of years-long marijuana consumption has been studied using the existing Coronary Artery Risk Development in Young Adults (CARDIA) program, which has over 5,000 adults aged between 18 and 30 enrolled.
The CARDIA program is now 25 years old and, among many others issues, its participants regularly report whether or not they used marijuana over the last month.
On CARDIA’s 25th follow-up, the participants were put through a series of cognitive tests checking their executive function, processing speed and verbal memory.
The initial results suggested that smoking weed worsened performance in all tests, but after adjusting the results to take into account other factors such as depression or the use of other substances, the researchers found that the only statistically significant correlation that could be established was between the long-term use of marijuana and verbal memory.
“We found a dose-dependent independent association between cumulative lifetime exposure to marijuana and worsening verbal memory in middle age,” the study said – meaning the more pot that’s smoked, the poorer the verbal memory results are.
The true mechanism of the effect has not yet been studied, but the researches made a supposition that marijuana’s main agent tetrahydrocannabinol affects information processing in the hippocampus part of the brain.
The findings of the study could not considered conclusive, however, as the participants provided no baseline data on cognitive abilities at the beginning of CARDIA, and only confirmed pot use verbally, passing cognitive tests only at the end of the study.
An editorial accompanying the study noted that people with originally lower cognitive abilities could be more likely to use marijuana – with corresponding results. Still, the editorial added, the general findings of the new study do correlate with previously available evidence that pot causes a decline in cognitive abilities and IQ scores, though this view has been contested.