Does Cannabis Really Affect Your Memory?

This article was originally published on Goldleaf and appears here with permission.

Yes, cannabis can affect your memory; it appears to promote both positive and negative effects. The nature and impact of these effects vary based on memory subtype, cannabinoid profile, age of user, and frequency of cannabis use.

Introduction

Although it’s an outdated trope, we’re all aware of the stereotype of the forgetful stoner. You know the type: the one who can never seem to find their phone. And keys. In extreme cases, perhaps even their car. 
But how much truth is there behind that caricature? 
Does cannabis impact a person’s memory in a detrimental way? 
Or maybe it’s the exact opposite? After all, cannabis is known to have a myriad of health-promoting effects for wellness.
Actually, the answer isn’t so cut and dry.
The latest research on the topic presents a complicated and still-evolving understanding of how cannabis influences memory function.
Although the science on cannabis and memory is far from conclusive, what has been discovered presents quite a bit of food for thought.
Read on to learn more about the key findings to date on cannabis and memory.   

What Is Memory?

Webster’s Dictionary defines memory as “a particular act of recall or recollection.” Simple enough, right? 
However, when examining the positive and negative effects of cannabis on memory, it’s important to delineate several different memory subtypes. This is useful because it appears that there’s quite a bit of divergence in effects depending on which memory subtype is being tested.
Prospective memory refers to a person’s ability to remember to perform a certain action at a specific time in the future.
Temporal order memory involves remembering the correct order in which a series of events occurred.
False memories are inaccurate recollections of past events. 
Free recall is a type of common memory test where information is given to a participant who later has to restate the data. It’s important to note that the ability to remember the order in which the information was shared is not an aspect of free-recall testing. 
Source memory refers to a person’s capacity to recall the origin of their memories or knowledge. For example, if you remember how to spell “receive” correctly because a teacher admonished you in front of your peers when you misspelled that word.
Working memory is an aspect of short-term memory that involves a person’s ability to remember things while occupied with a task. 
Now, with these definitions established, let’s proceed to an analysis of the latest research on how cannabis affects memory.

What Positive Effects Does Cannabis Have on Memory?

Although it may be surprising to some, cannabis has been shown to have positive effects on memory in specific instances.

Faster Processing Times With CBD

A 2020 study conducted by researchers at University College London found that a single dose of 600 mg oral CBD was associated with faster response times on memory tests in healthy individuals.
The reason for this appears to be because CBD increases cerebral blood flow to the hippocampus, which is thought to be the most important region of the brain for memory.
The implications of this study (and others) are quite promising for treating Alzheimer’s, epilepsy, schizophrenia, post-traumatic stress disorder, and other conditions that have neurodegenerative effects.
It is worth noting, however, that the researchers found no difference in accuracy on the memory tasks between the group receiving CBD and the control group.

High-CBD Cannabis Does Not Impair Memory

The study from University College London indicated that CBD may have positive effects on memory. 
But what if you decide to consume cannabis directly, rather than only CBD?
In that case, cultivars with significant CBD content may be a good option if you’re concerned about potentially detrimental effects on your memory.
A study from 2020 confirmed that memory accuracy was not impaired when using cultivars with both THC and CBD.
However, that same study found that those who used cannabis cultivars and products without CBD faced substantial acute and long-term challenges with memory accuracy.

The Older You Are, The Better Cannabis May Be For Your Memory

The latest research seems to lead to the conclusion that CBD may have slight benefits for memory (or, at the very least, to not be harmful to your memory).
Unfortunately, much of the research shows THC may have negative effects on memory.
However, a 2017 study in which mice were given THC contradicted the general picture painted elsewhere.
This study demonstrated that older (18 month old) and mature (12 month old) mice performed as well as young (2 month old) mice on a series of memory tests after they received a small dose of THC.
Furthermore, the researchers discovered that it was THC’s interaction with the hippocampus in these older and mature mice that resulted in this beneficial effect.
Conversely, the administration of THC to young mice led them to perform worse on memory tests.
Additional study may indicate that THC impacts human memory in a similarly age-dependent fashion. 

Many Types of Memory Are Not Adversely Affected By Cannabis

Although some of its findings were cause for concern, a recent study by researchers affiliated with Washington State University uncovered two positive effects related to cannabis and memory.
The researchers found that cannabis use was not correlated with a decline in prospective memory, as participants who used cannabis and those who remained sober performed about equally.
Additionally, cannabis users in this study performed well on tests related to temporal order memory.
Interestingly, these results were consistent regardless of whether participants consumed high-potency flower (i.e. 20% or more THC) with CBD, high-potency flower without CBD, or high-potency concentrates (i.e. 60% or more THC) with CBD.

A Few Objections Worth Considering

Current research seems to indicate that cannabis has detrimental effects on some types of memory in certain instances. 
It’s also true that researchers are held to a high standard by their peers through the process of peer review; studies with overt weaknesses in methodology are unlikely to be published in respected journals. 
That said, cannabis is not the only substance that may impair memory. Alcohol, which is both ubiquitous in our society and fully legal, can lead to memory loss and brain damage.
And alcohol is just one of numerous legal and illegal substances that can impair memory. 
Even if research participants are not currently under the influence of any substances besides cannabis—which nearly all studies do control for—there is the potential that past use of such may have created lingering effects.
A related concern is rarely discussed: that people with prior memory impairment may not be fully aware of their history with other substances. In turn, this might skew the data and lead to inaccurate conclusions.

What Negative Effects Does Cannabis Have on Memory?

Although cannabis may produce beneficial effects on memory in particular situations—especially for older individuals or those suffering from neurodegenerative disorders—various studies have shown that cannabis may produce harmful effects as well. 
Revisiting The Washington State University Study 

Earlier in this article we discussed the positive effects of cannabis on memory that were discovered in a study funded by Washington State University’s Alcohol and Drug Abuse Research Program.
Now it’s time to discuss the negative effects of cannabis on memory that were found in that same study of current cannabis users.
One concerning discovery was that people who used concentrates with a THC content of 10% or higher were more likely to have difficulties related to false memories, source memory, and free recall.
Another cause for concern was that this study contradicted what other researchers had found regarding CBD’s ability to protect against harm to memory.
The data from this study showed that those who smoked flower with CBD did worse on verbal free recall tests than the sober control group. Interestingly, they also performed worse than those using concentrates or flower without CBD.
Furthermore, the team from Washington State University also found that users of high-potency concentrates and flower devoid of CBD performed worse on tests of source memory. 
Lastly, this study also revealed that all cannabis users—those using concentrates, flower with CBD, and flower without CBD—had poorer results on a false memory test than those who were sober.
It is important to state that this is merely one study among the relatively small number of studies on cannabis and memory. Moreover, the study was limited to those who were already heavy users of cannabis.
But the report itself indicates the results may not be that alarming: “Despite the use of high-potency products, we failed to detect any significant effects on any of these [memory-related] outcomes. It is possible that this reflects a true absence of effects of cannabis on these aspects of cognition.”
There is one final point to note: This study measured how cannabis interacted with memory while high. 
An intriguing follow-up study would be to measure performance on this array of tests by cannabis users who are stoned, cannabis users who are sober, former cannabis users who are sober, and those who are sober and have never used cannabis.

Frequent Cannabis Use and Memory

In 2020, a research team led by Monica E. Lovell conducted a meta-analysis of thirty studies that had assessed the impact of cannabis on memory. 
Altogether, Lovell et al.’s study examined differences in memory and cognition between the 849 research participants who used cannabis and the 764 participants placed in control groups.
All cannabis-using participants in the studies selected by Lovell’s team were long-term (mean of 2 years), frequent (mean of 4 days per week) recreational users who had abstained from consuming cannabis for an average of 12 hours.
What Lovell’s team found were small, albeit significant, differences in memory between the cannabis users and those in the control groups.
Specifically, their findings indicated that frequent users of cannabis performed poorer on assessments related to memory, inclusive of working memory, attention, and information processing.
Perhaps most concerning about Lovell et al.’s meta-analysis was that this gap between cannabis users and sober individuals remained intact even when adjusting for cannabis use duration, age of onset, and lengthy abstinence from cannabis use.

Conclusion

According to the current research, it appears that cannabis promotes both beneficial and harmful effects on memory.
However, there are numerous instances of similar studies that contradict each other’s findings. 
It’s unlikely that further research will lead to our being able to make a conclusive blanket statement, such as that cannabis improves or protects memory. 
Even so, additional study may prove promising in helping the scientific community gain more clarity on the complex ways that cannabis impacts memory.