Is Memory Reliable When High? New Study Finds a Troubling Link Between Cannabis Use and False Memory

The use of cannabis is linked with an increased susceptibility to forming false memories, according to a new study published in Proceedings of the National Academy of Sciences (PNAS).

There exist two kinds of false-memory – “spontaneous” false memories – which arises due to internal cognitive processes – and “suggestion-based” false memories – which occurs due to external suggestion.

In this double-blind, randomized, placebo-controlled trial, the researchers assessed both the immediate and delayed effects of tetrahydrocannabinol (THC) intoxication on susceptibility to false memory in 64 healthy, occasional cannabis users (32 male, 32 female, mean age, 23). On separate test days, each subject inhaled either a single dose of cannabis (300 μg of THC per kg of body weight) or a placebo. Subsequently, each participant was tested on their capacity to encode and retrieve memories while intoxicated and then tested on their ability to retrieve memories one week later when sober. The researchers used three different study methods to test each participant: associative word lists; and two misinformation tasks which assessed the volunteers’ memory using virtual reality.

Troubling Link and Possible Implications

According to the results of the study, the researchers observed increased false memory effects in participants who were under the influence of cannabis. They noted that specifically, intoxicated participants exhibited higher false recognition when completing the associative word-list task both at immediate and delayed intervals compared to subjects in the control group. Moreover, in a misinformation task, the researchers observed that intoxicated participants were more susceptible to false-memory creation using a virtual-reality eyewitness scenario and virtual-reality perpetrator scenario.

“With the growing global acceptance of cannabis and its widespread use by eyewitnesses and suspects in legal cases, understanding the popular drug’s ramifications for memory is a pressing need,” the research authors wrote.

“Cannabis-intoxicated witnesses and suspects pose a vulnerable group and might profitably be identified as such, and while drug testing is a routine procedure with suspects, this is not the case for witnesses or victims. Although cannabis is oftentimes connected with positive effects (e.g., pain reduction), it might also lead to hazy memories, which eventually opens the door for a negative effect: increases in false memories.”

The researchers added that their findings have “implications for how and when the police should interview suspects and eyewitnesses.”