Cognitive effects in midlife of long-term cannabis use



Cannabis has been used for several thousand years, since the beginning of history. It started as a plant for medicinal purposes and is currently used by about 25% of Americans who use it on a regular basis. Cognitive effects in midlife of long-term cannabis use are still debatable, but there are some important facts that can be gained from long-term cannabis users in midlife reported studies.

Cannabis users have been shown, in clinical trials, to experience similar effects as those experienced by long-term alcohol users. This article explores how cannabis use may negatively affect cognitive functions during midlife and how this effect is different from other substances.
A study published in October by the Journal of Experimental Psychiatry investigates the long-term effects of cannabis on cognition. The study found that regular cannabis use can cause poor cognitive performance during midlife, but not immediately after use had ceased.

Executive Function

Executive function is the set of mental processes that allow us to plan, organize, and manage ourselves. The same functions are involved in many other aspects of our lives, including the decision-making process.
The prefrontal cortex is a region of the brain that plays an important role in executive function. It is located just behind your forehead, just below your eyes and above your nose, in front of the midline of your brain.
The prefrontal cortex is involved with tasks such as working memory (keeping information active in short-term memory), planning ahead for the future and making plans for short-term goals.
In cannabis users, there is evidence of impairment on tests measuring executive function such as Trail Making Tests A and B (TMT A & B).
Executive function is the ability to control your thoughts and actions. It’s a set of thinking skills, such as attention, focus, problem solving and memory. These skills are important for everyday activities such as driving and managing finances.
Cannabis users may have problems with executive function because their brain chemistry changes when they use cannabis. This can affect:
Cannabis use can impair executive function, which is the ability to plan, organize and prioritize tasks. This can lead to problems with working memory and attention.


Long-term cannabis use is associated with memory impairment, but it is unclear whether the cognitive effects of cannabis result from alterations in-memory processing or in the accuracy of memory representations. In this study, we examined how long-term cannabis use affects both cognitive processes and memory for words. We then evaluated potential underlying mechanisms by testing the effects of acute administration of Δ9-tetrahydrocannabinol (Δ9-THC) on word recognition and associative learning in healthy individuals.
We found that long-term cannabis users exhibited poorer memory performance compared with non-users. However, there was no difference between groups in the accuracy of their word representations, indicating that these differences may not be due to an altered encoding of information per se. Instead, we propose that such deficits are reflective of a selective attentional bias toward tasks requiring more effortful processing and/or a decreased capacity for maintaining information over time.
These findings suggest that long-term cannabis use may affect cognitive performance by disrupting attentional processes rather than disrupting word representations directly: it may be that frequent users are unable to sustain focus on tasks requiring more effortful processing or have difficulty maintaining relevant information at both encoding and retrieval stages.
The age-related decline in memory is a well-known fact. This decline has been attributed to factors such as lifestyle, stress and depression, but there are also studies that suggest cannabis use may be associated with the same issue.
A recent study conducted by researchers at the University of Montreal and published in The Journal of Neuroscience looked at the relationship between cannabis use and cognitive function in midlife.

Processing Speed

Processing speed is the ability to process information quickly and accurately. It is the ability to recognize patterns, make decisions and solve problems. Processing speed declines with age.
Processing speed is related to many areas of cognition and behavior. For example, processing speed is related to attention and memory as well as problem-solving and decision-making.
A study conducted by Jobe et al (2011) investigated how cannabis affects cognitive performance in long-term users compared to non-users. The study assessed participants’ processing speed by having them complete a series of tests designed to measure their reaction time and accuracy in performing simple tasks such as reading words or performing math calculations. The results showed that long-term cannabis use had a negative effect on processing speed compared to non-users (Jobe et al 2011).
The processing speed of a worker is a key factor in their productivity. As we age, our processing speed slows down. This is why it is so important for workers to stay as physically active as possible to preserve their cognitive function and prevent dementia from setting in.
Long-term cannabis users have more trouble with processing speed than non-users. For example, they are less able to recognize patterns and make connections between similar things and have more difficulty performing simple tasks such as sorting cards into groups or following instructions.
While processing speed is not directly related to IQ, it can be measured by a number of tests that measure how well you can perform basic calculations in your head (e.g., multiplication tables). These tests can be used to measure the effects of cannabis on processing speed.


Researchers found that persistent cannabis users displayed deficits in attention, verbal learning and memory, and psychomotor speed when compared with non-users. Their results suggest that long-term cannabis use has a detrimental effect on cognitive functioning in early midlife. These findings suggest that cannabis use in adulthood can be associated with cognitive impairment in midlife and a reduction in the age of onset of cognitive impairment.
In other words, they were not drawing conclusions as to whether or not marijuana causes cognitive decline. Rather, they were simply reporting that cognitive decline is possible with heavy cannabis use in midlife. That’s somewhat discouraging to hear, especially since so many people will smoke marijuana without realizing that it could potentially have a long-term impact on their ability to remember things and process information.

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