Can Smoking Cannabis Damage Your Brain Cells?
A scientific insight into arguably the biggest debate surrounding the drug.
When Matthew went to the local Stop & Shop that warm summer morning to buy a couple of avocadoes and a Doritos packet, he returned home only with the tortilla chips, completely forgetting about the other product he went to the supermarket for. The week after, for a couple of days in a row, Matthew kept completely forgetting his appointments with his friends, his girlfriend, and his dentist.
He had always considered himself a daydreamer, which sometimes, he said, was a problem, as he wasn’t really able to fully focus on his daily tasks. However, his forgetfulness and absentmindedness had become a “glitch in his system.”
Normally, forgetting such minor stuff wouldn’t be considered a problem if it was a rare occurrence. Right?
Matthew told me back then that this had started happening daily — he would constantly forget what he had planned to do the same day, would be extremely absent-minded and not be able to concentrate on even the simplest of tasks. The biggest problem was that he was starting to feel that he was becoming dumber.
But why? I asked. It was simply because, he told me, he had been smoking cannabis daily for the past 1 year. By “daily” he meant 2 joints Every. Single. Day. Matthew felt as if his brain had started to melt down and expressed his fears that “much of his brain cells have died.”
I then thought: “Well, that’s not the first story I hear about how smoking cannabis had affected one’s mind in such a way.” I had spoken to a lot of people who used it on a daily basis and the accounts of their experiences varied — some said it hadn’t affected them at all, whereas others told me similar things to Matthew’s case.
So, I thought, there ought to be a pattern between them all. It was either that these guys (and gals) smoke so much weed and are used to it at the point where they cannot see the ill effects, or the ones that said they didn’t experience any downturns, could not really identify them, as probably this brain-activity degradation is a slow, gradual process.
These are my assumptions, though. But what does science say about all this?
But Really, Can Smoking Weed Reduce Your IQ?
Ever since I’ve found out about cannabis, the argument of whether smoking it impacts your IQ has been a recurring topic. Most of my friends have told me that they see no difference in their intelligence, although having not taken an actual IQ test. “I’m as smart as before,” one of them would say. Others, though, expressed their concerns about how they felt a little bit more absent-minded than usual, however, didn’t feel any less intelligent.
A renowned study from the last decade conducted in New Zealand, involved 1037 participants, which were followed from birth (1972/1973) to 38-years-of-age, argued the following:
- Persistent cannabis users show neuropsychological decline from childhood to mid-life;
- Individuals, who started smoking cannabis daily during their adolescence and then continued the same practice as adults, had lost and average of 6 to 8 points of IQ, by their mid-life;
- Individuals, who started using weed on a daily basis in their adult years, didn’t lose any IQ points;
- Stopping the usage of marijuana during their mid-life, individuals didn’t regain any lost IQ points;
Although the study presumably had strong evidence that showed the consumption of cannabis, based on the findings, has a neurotoxic effect on the individual’s adolescent brain, it had its limitations.
A counter-study the following year, conducted by Michael Daly, back then a behavioral scientist at the University of Stirling, argued that there was one variable that was omitted: the stable individual differences in personality traits, which could possibly cause both drug use and changes in intelligence in the individuals examined.
The cannabis-intelligence link, Daly argued, may be highly affected by such personality traits. For example, the sometimes negative connection between consuming marijuana and low neuropsychological results may stem from the individual’s low conscientiousness, which could, in turn, lead to substance dependence and low results on the IQ tests.
Similar research had been conducted on rats by Patrizia Compolongo (and her colleagues), a professor of Physiology and Pharmacology at the Sepienza University of Rome. The results showed that when young and adolescent rats were exposed to THC, experienced notable problems with “specific learning and moment tasks” later in their existence.
In yet another study, this time on monkeys, the results showed that there are obvious short-term impairments on working (temporary) memory for adult users who had used cannabis. Nevertheless, the ill effects that occurred from 7 to 20 hours after exposure, were less significant for adult users than for the adolescent ones.
Age Matters
All the studies on cannabis and its effects on the brain, no matter how much they vary in their findings, and no matter whether they were conducted on humans or animals, they touch upon one common ground — adolescents’ brain could be way more vulnerable than the adult’s one, after being exposed to cannabis usage.
Further, one study argues, the initiation of marijuana usage during the years of adolescence may result in lower IQ levels in adulthood. Ultimately, upon reaching the mid-life range, regaining lost IQ due to weed consumption happens to be improbable.
On the other hand, a study from 7 years ago argued that chronic cannabis usage could have an altering effect on the structure and functions of an adult’s and adolescent’s brain. Another study, done in the same year, showed that weed users had a consistently smaller hippocampus than individuals who hadn’t consumed the drug.
*To clarify — the hippocampus is the region of the brain that is associated primarily with learning and memory, which are closely related to IQ.
Furthermore, in 2016, a 25-year-long study on cannabis, showed that cumulative drug exposure was related to lower results on a verbal memory test, however, it did not affect other cognitive abilities, such as processing speed or executive function.
The Bottom Line
Though many studies so far have been conducted on the better understanding of cannabis and its effects on our brains, no final unifying conclusion has thus far been made. However, there are some commonalities between all of the research documents:
- Adolescent individuals’ brain are far more vulnerable to cognitive alterations to adults’ ones, after being exposed to cannabis usage;
- Neuropsychological decline is seen from childhood to mid-life, considering the cannabis consumption had been initiated at a sooner age and persisted throughout growing up;
- The hippocampus — the part of the brain associated with memory and learning — happens to be negatively affected by cannabis consumption;
Nevertheless, no matter how many studies have so far been conducted, the connection between smoking cannabis and the decline in IQ is still blurred, as there are numerous factors to be taken into consideration that can influence the results — genetics, frequency of use, age of the first usage, duration of usage, climate, and so many more.
Although most studies point towards the assumption that smoking cannabis does affect your brain in an ill way — by messing up with its cognitive functions — concrete evidence is still needed to support the claim.
It’s a positive thing to see that more and more interest has been now put on such substances, however, the whole range of both negative and positive effects of cannabis are yet to be fully understood.
Thank you for taking some time to read my article! If you wish to read more written by me, check my Medium page:
I write about psychedelics and mental health. Recently, I wrote an article on whether being high makes you dumber and an interview with a current LSD user:
