Long-term cannabis use damages memory by disrupting sleep, study finds

New research from The University of Texas at Dallas reveals that long-term cannabis use may trigger a chain reaction that harms memory by disrupting sleep quality.

The study, published in the American Journal of Drug and Alcohol Abuse, explored the complex relationship between long-term cannabis use, sleep quality, and memory. Unlike prior research that examined sleep and memory in isolation, this investigation provides a new understanding of how these factors interact.

The urgency of the findings was highlighted by Dr. Francesca Filbey, professor of psychology at UT Dallas, who noted that as cannabis legalization expands across the US, “how little we know about its effects remains the same.”

The study compared 141 adults diagnosed with Cannabis Use Disorder (CUD) against 87 non-current users. Crucially, participants had abstained from cannabis for 24 hours before testing to eliminate the immediate effects of intoxication and ensure the accuracy of the results.

The key discovery was a specific pathway of harm: The researchers found that long-term cannabis use does not primarily damage memory directly. Instead, it degrades the quality of sleep, and this sleep impairment is what, in turn, weakens the brain’s ability to retain new information.

“The individuals with CUD who reported more problems with sleep were the ones having poorer memory outcomes,” explained lead author Tracy W. Brown. “We’re discovering that cannabis’s indirect effect on cognitive outcomes is tied to how cannabis impacts the regulation of the sleep cycle.”

Spatial vs. Verbal Memory

Surprisingly, the study found the impact was most severe on spatial memory—the ability to navigate and remember locations—rather than verbal memory.

Brown attributes this to how cannabis alters specific sleep phases. “Typically, long-term cannabis use impacts slow-wave sleep, which, outside the context of cannabis, affects hippocampal function,” Brown said.

Unlike total sleep deprivation or insomnia, which typically result in verbal memory deficits, cannabis reduces the quality and depth of sleep needed for spatial processing.

Risks for Young Brains

The study underscores important risks for users under 25, whose brains are still maturing. Dr. Filbey warned that relying on cannabis for sleep can lead to dependency and tolerance, requiring higher doses for the same sedative effect, further disrupting natural sleep cycles.

“When use begins in adolescence, sleep deficits are usually much more pronounced,” Filbey added. “People need to be aware of this.”