Does Cannabis Affect Memory Consolidation or Cognitive Function? Here’s the Final Say on All the Studies So Far
Study finds daily cannabis users able to recall an average of 0.5 less words from a memory list. Gasp. And no other decline in cognitive function.
It’s well-documented that cannabis can affect short-term memory. Studies show that while cannabis is “active” in the body, people’s sense of recall slips a bit (this is on par with antidepressants, antihistamines, anti-anxiety medicines and pain medicine). But what about the rest of it — can cannabis turn a stroll down memory lane into a stumble?
First, let’s acknowledge that memories are notoriously fickle things. Police, hypnotists, psychiatrists and gas lighters of all kinds already know that most human memories are not etched in stone, but rather subject to change. People can be convinced that false memories implanted by researchers really happened. Through suggestion, people can come to believe childhood milestones occurred differently from what really happened. The malleability of memory may be an evolutionary advantage — or a saving grace (if you’re cynical), but either way, it’s a property that makes the subject downright difficult to study.
And it’s not just the malleability. Memory can be affected by everyday problems like a fitful night of sleep or poor nutrition, which makes it even more difficult for researchers to pinpoint any one things as the cause of memory lapses.
Luckily, scientists have developed standards for memory research to ensure that what we study presents the best picture of what we know about memory, even if it may be incomplete. For instance, credible memory studies do not directly imply causality if none exist. Another breakthrough is the use of the increasingly popular field of brain science, which allows researchers to use hard data on electrical activity happening within the brain to show memory effects, rather than relying on patient surveys.
Thanks to brain science, we know that memory impairment from cannabis occurs (partially) from the way that THC affects the hippocampus, which is a region of the brain responsible for memory formation and information processing.
A study published recently in JAMA Internal Medicine tested heavy cannabis users’ memories against the recall abilities of people who never, or rarely, use cannabis. The results showed that heavy cannabis users have less vigorous short-term memory — but only slightly.
How slight? After hearing a list of 15 words, heavy cannabis users (those who smoked for every day for a year) were able to recall 8.5 words from the list on average. Their non-using counterparts averaged 9 out of 15. That’s not much of a difference — although the researchers noted that the effect could increase for users who smoked daily for a more than one years.
The study also noted that there were no other declines in cognitive function or concentration abilities in heavy cannabis users, a refrain form an 2003 study that concluded: “Although there are signs of mild cognitive impairment in chronic cannabis users there is little evidence that such impairments are irreversible, or that they are accompanied by drug‐induced neuropathology.” In layman’s terms, this means that cannabis slows down brain functioning while it’s active, but the change is only temporary.
A massive study of cannabis and brain function was undertaken in 2013 as a way to “update” the earlier science and provide a more clear-headed picture of cannabis’ effects. It found that the cannabidiol (CBD) in cannabis dampens THC’s effect on episodic and spatial memory — and that frequent users may have a higher tolerance to THC’s memory impairing properties. It also suggested that genetic factors could play a significant role in how cannabis affects all brain functions, including memory, in individuals.
The best data collected on long-term memory impairment comes from the journal JAMA Psychiatry, which followed hundreds of adult cannabis users aged 30-55 and divided them into three groups: Chronic users, who smoked daily; former chronic users who only occasionally smoked cannabis, and a control group who had used cannabis less than 50 times.
The study design was simple: Participants were given a word recall test on day 1, then asked to abstain from cannabis for 28 days. After the first day, participants were tested again one day later, then seven days later, and finally again the full 28 days.
Initially, chronic cannabis users performed worse than the other two groups. After one week, the chronic users were still behind the others by a significant amount, but by Day 28, there was no discernable difference between the chronic users and the control group. The researchers concluded that whatever effects cannabis has on short-term memory are themselves short-lived — at least in adults.
Many studies have pointed to changes in the brains of younger cannabis users, who may have lasting damage by chronically using cannabis while their brains are still rapidly developing. The research cannot fully support that idea, but it is embraced by the scientific community.