Studies Suggest Cannabis May Create a False Memory Effect

Matt Weeks February 26, 2020 0 comments

New research is questioning the powers of recollection for cannabis consumers.

Human memory — on it best day — is much frailer than many like to admit. Every day, people forget important information, blank on the names of important persons in their lives, and lose their train of thought mid-sentence. Even worse, we straight up remember stuff differently than how it happened. That’s called the false memory effect.

The authors of a new study on the false memory effect, published in PNAS (2020), argue their work has implications for police work. The suggestion is that when and how police interview suspects and eyewitnesses should take into account cannabis consumption. But, this study on the false memory effect may have even broader implications for medical patients, recreational consumers, and an increasingly cannabis-accepting society.

How Does Cannabis Effect Memory?

This isn’t the first time someone has associated cannabis with memory issues. THC, the active intoxicating chemical in cannabis, has long had links with weakened memory. Thankfully, most of the more negative stereotypes are no more than stereotypes.

Several studies suggest that while THC can affect memory (in both positive and negative ways) research published in Psychopharmacology (2002), found these are short-lived and dissipate forty-eight hours after cannabis consumption.

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That doesn’t sound like a big problem. But, the new research didn’t look at whether or not THC can contribute, however briefly, to a poorer memory recall. It examined whether or not THC makes consumers susceptible to the false memory effect. Instead of testing if participants could remember a list of words correctly, it examined whether they would identify new words inserted into previously studied lists as being there all along.

The difference is important. Perfect memory recall and susceptibility to the false memory effect are both important facets of memory function. But, they come from different places in the brain, and produce different outcomes in society.

To further explore the revelations of this new study on the false memory effect, it’s important to look back at the authors’ older work first.

false memory effect could interfere with this young man's thoughts

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Finding the False Memory Effect

The new memory research builds off the authors’ previous work on THC and memory. In 2019, they published a different paper in Psychopharmacology that found interesting results.

This earlier study aimed to find out if there was a link between cannabis and the production of false memories. The researchers enlisted the help of 150 volunteers.

  • One-third of them were regular cannabis consumers who were under the influence of THC at the time of the test
  • Another third were regular cannabis consumers who were sober at the time of the test
  • The last third were lifelong abstainers from cannabis.

In the test, the participants studied word lists related to a non-presented word. For example, a list may contain the words “waiter,” “table,” “menu,” “food,” “drinks,” and “bill” without including the word “restaurant.” Later, the participants had to recall which words were on the lists. However, this time the inclusion of the associated word (“restaurant” in the above example) occurred.

After testing all three groups, the researchers found that the ability to identify the newly inserted associated words (like “restaurant”) were not statistically different between the groups. In other words, there was no association between THC consumption and producing false memories. However, the cannabis consumers fared slightly worse on recalling the other words in the original research. So, what did the new research add? Quite a bit, it turns out.

Spontaneous False Memories vs Suggestion 

False memories come in two flavors: “Spontaneous” false memories come from jumbled internal cognitive processes, and “suggestion-based” false memories that occur because of external suggestions. As the earlier study proves, cannabis does not cause consumers to create spontaneous false memories. However, the newer research shows that cannabis consumers are more likely to have problems with suggestion-based false memories.

To find out how THC affects suggestion-based false memories, the researchers decided to investigate the issue from a different angle. Instead of having participants look over lists of words, the researchers subjected their volunteers to a fake event (a mock crime), then exposed them to false information about the event through leading questions and conflicting stories from other witnesses. Then, the participants took memory tests.

Later, they experienced the mock crime again, but as perpetrator instead of a witness. Half participants were tested immediately after consuming THC, the other half were sober. The THC group were more influenced by the leading questions and other eyewitness testimony according to the research. And more frequently claimed to have witnessed things that never happened.

Interestingly, when the participants underwent the same test one week later, this time without cannabis, the group that first consumed THC were still more susceptible to the false memory effect.

false memory effect could influence this woman's thoughts about the car accident scene behind her

What Does it Mean? 

The researchers point out that this discovery may not have great applications — except in cases of police work. And even then, there isn’t yet research to prove that the effect is the same.

Overall, the participants who consumed THC were more likely to agree with false remembrances made by the other eyewitness than to rely on their own recall. It’s possible this is related to how cannabis affects memory, but it’s just as likely a result of how cannabis affects social skills. The THC consumers may have been more agreeable in general, and wanted to believe the other witnesses.

It’s also possible that because people believe THC causes memory problems, they’re more likely to take someone else’s word over their own when trying to remember the truth about an incident. Most likely, however, THC interferes with memories a bit. The authors rightly conclude that police should account for this when they interview eyewitnesses or lean hard on suspects whose memories seem spotty.


Curran, V.H., Brignell, C., Fletcher, S. et al. (2002). Cognitive and subjective dose-response effects of acute oral Δ9-tetrahydrocannabinol (THC) in infrequent cannabis users. Psychopharmacology 164, 61–70. https://doi.org/10.1007/s00213-002-1169-0
Kloft, L., Otgaar, H., Blokland, A. et al. (2019). False memory formation in cannabis users: a field study. Psychopharmacology 236, 3439–3450. https://doi.org/10.1007/s00213-019-05309-w
Lilian Kloft, Henry Otgaar, Arjan Blokland, Lauren A. Monds, Stefan W.Toennes, Elizabeth F. Loftus, Johannes G. Ramaekers (2020). Cannabis increases susceptibility to false memory.
Proceedings of the National Academy of Sciences. 201920162; DOI:10.1073/pnas.1920162117
Author avatar

Matt Weeks

A writer living and working in Athens, GA, Matt's work has appeared in various newspapers, books, magazines and online publications over the last 15 years. When he's not writing, he hosts bar trivia, plays in local bands, and makes a mean guacamole. He holds an undergraduate degree in journalism and a master's degree in organizational theory. His favorite movie is "Fletch."

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