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Is weed making you more susceptible to false memories?

The trope of the forgetful stoner exists for a reason: sometimes consuming the plant can impair our memory. But what if cannabis has other effects on our ability to recollect? What if it makes us create memories that aren’t real?

New research shows that the plant’s most recognized ingredient, tetrahydrocannabinol (THC) could make us more prone to forming false memories.

A team of researchers at a university in the Netherlands wanted to know what effect cannabis had on memory formation. Led by Lillian Kloft at the faculty of Psychology and Neuroscience at Maastricht University, the researchers conducted a double-blind, randomized, placebo-controlled trial to examine the way THC affects how susceptible we are to false memories.

Published in the journal Proceedings of the National Academy of Sciences, the trial was set up to test participants’ memory after either THC intoxication or exposure to a placebo. Participants (64 healthy individuals in total) were tested for false memories immediately after consumption, and then again one week later.

Testing their memories involved two tasks: the first had participants examine a list of 15 related words. Scientists conducting the trial found that those who were administered THC were more likely to say they recognized particular words that they had not actually been shown, than participants who had been given the placebo.

Scientists utilized virtual reality for the second task, which tested participants’ ability to correctly answer questions after first witnessing, and then perpetrating a crime (a fight at a train station and handbag theft).

Next, participants were asked to answer a set of questions about the different scenarios. Researchers deliberately included misinformation and posed questions that may have suggested an alternative course of events.

As it turns out, Kloft’s team found that the group of participants exposed to THC were much more vulnerable to forming false memories. When participants were tested a week following the initial trial, the results were the same: those who were given THC had the same susceptibility to false memory formation.

According to researchers, their work could have serious implications in the legal system, particularly in cases that rely on the testimony of eyewitnesses.

“In terms of interviewing witnesses, victims, or suspects after the incidence of a crime, this means that interviewing while the individual is still intoxicated should be minimized, due to elevated risk of false reporting,” they conclude.

The researchers go on to suggest that questioning should “ideally take place as soon as the person has sobered up to prevent memory decay due to time”, but add that a person under the influence of cannabis “might still show a yes bias toward some new information later.”

“Thus, cannabis-intoxicated individuals might have to be treated as a vulnerable group, similar to child or elderly witnesses/suspects.”

This article is available under a Canadian Creative Commons licence.