New research suggests that cannabis users tend to be more likely to forget to remember to perform tasks when facing stressful conditions. The findings have been published in the journal Psychopharmacology.

“We were interested in this topic because trends toward the legalization of cannabis in North America have increased access to cannabis and diminished perceived risks of harm,” explained study author Carrie Cuttler, an assistant professor at Washington State University.

“We recently discovered that relative to non-users, cannabis users demonstrate a blunted stress response to a multidimensional stressor and we wanted to further investigate whether an acute stressor would differentially impact the prospective memory test performance of cannabis users and non-users.”

“Prospective memory is our ability to remember to execute tasks in the future (e.g., pick a child up from school, take medication on schedule) and is critical to our ability to function in everyday life,” Cuttler told PsyPost.

“Research regarding the impact of cannabis use on prospective memory has been largely mixed. Further, previous research has indicated that acute stress may facilitate prospective memory performance. Given that chronic cannabis users demonstrate a blunted stress response, we reasoned that this might translate into impaired prospective memory task performance in chronic cannabis uses.”

For their study, the researchers compared 40 cannabis users to 42 non-users. The cannabis users had used the substance a minimum of 3–4 times per week for at least one year. The non-users, on the other hand, were required to have not used cannabis in the past year and to not have used cannabis more than 10 times in their lifetime.

The participants provided the researchers with an important belonging, such as their keys, which was then locked in a drawer. The researchers instructed the participants to request the return of the item after they had finished a series of psychological tests and surveys.

During the series of tests, the participants were randomly assigned to complete 5 trials of either the high-stress or no-stress version of the Maastricht Acute Stress Test (MAST). The participants were asked to try to remember to indicate how painful they found each trial.

In the no-stress version, participants placed one hand in lukewarm water for 45-90 seconds and then were asked to count from 1 to 25. In the high-stress version, participants placed their hand in ice cold water for 45-90 seconds. They were then asked to count backwards from 2043 by 17 and were given negative verbal feedback when they made a mistake.

The researchers found evidence that higher levels of stress were associated with worse prospective memory performance. But, like previous research, the findings on cannabis were mixed.

Participants who scored higher on a self-reported measure of chronic stress were more likely to forget to ask for their belongings back, regardless of whether they were cannabis users or non-users.

Similarly, participants in the high-stress version of the MAST were more likely to forget to indicate how painful they found each trial. But in this test, cannabis users tended to be more forgetful than non-users.

“Our findings indicate that acute stress was detrimental to prospective memory task performance and that this effect was magnified in chronic cannabis users. Therefore, chronic cannabis users may be more likely than non-users to forget to perform tasks under conditions of stress,” Cuttler told PsyPost.

The cross-sectional nature of the study forces the researchers to stop short of making any determinations about causality.

“We are not able to manipulate chronic cannabis use in humans so we cannot definitively conclude that chronic cannabis use caused the stress-related detriment to prospective memory task performance,” Cuttler explained.

“Instead, we can only state that chronic cannabis use is associated with stress-related detriments to prospective memory task performance. We also still need to better understand the mechanisms underlying this effect.”

The study, “Joint effects of stress and chronic cannabis use on prospective memory“, was authored by Carrie Cuttler, Alexander Spradlin, Amy T. Nusbaum, Paul Whitney, John M. Hinson, and Ryan J. McLaughlin.