“Although sleep is one of the primary reasons people use cannabis, our findings suggest that long-term cannabis use actually results in poorer sleep, which is associated with poorer memory.”
~ Tracy Brown, Psychology PhD student, University of Texas at Dallas
Although many people are prescribed medical marijuana to help them sleep, a recent cooperative study between the University of Texas at Dallas and the University of Amsterdam found that long-term cannabis may in fact have the opposite effect.

The First Study of Its Kind

While earlier research looked separately at the impacts on sleep and memory, this study focused on both. Published in June in the American Journal of Drug and Alcohol Abuse, it focused on these three interrelated factors.  The first study of its kind, it relies on long-term marijuana use.
In this study, 141 adult subjects with a previous diagnosis of Cannabis Use Disorder and 87 non-current cannabis users were included in the study. To avoid skewing the results due to the drug’s acute effects, none of the subjects had used marijuana within the previous 24 hours.

Marijuana, Poor Sleep, and Health Problems

“At this time there still isn’t any clear evidence that cannabis is helping sleep. We know that when people initiate use there is some benefit in the immediate short term, but there is quick tolerance to this effect. There currently is no good quality evidence to suggest that cannabis will help improve sleep quality or duration.”
~ Dr. Bhanu Prakash Kolla, MD, Center for Sleep Medicine, Mayo Clinic
As reported in earlier studies, regular marijuana use seems to harm sleep. This describes a long-term study published in Regional Anesthesia & Pain Medicine.  It found that adults who use cannabis 20 or more days a month are:
• 64% more likely to get less than six hours of sleep a night
• 76% more likely to sleep more than nine hours a night.
The Centers for Disease Control and Prevention defines optimal sleep for adults as 7 to 8 hours per night
Even moderate marijuana use increases the risk of potentially problematic sleep. Occasional users are 47% more likely to sleep more than 9 hours per night.  Those with CUD do not fare so well.

Marijuana, Poor Sleep, and Memory

“…the individuals with CUD who reported more problems with sleep were the ones having poorer memory outcomes. We’re discovering that cannabis’s indirect effect on cognitive outcomes is tied to how cannabis impacts the regulation of the sleep cycle.”
~ Tracy Brown
The research team found that marijuana’s impact on the sleep cycle in turn negatively affected users’ spatial memory – which helps them navigate directions and remember where things are located.
Interestingly, disrupted sleep did not affect verbal memory.
“Sleep disruption from cannabis use isn’t necessarily insomnia-related or complete sleep deprivation.  Rather, it’s a reduction in the quality of sleep. Full sleep deprivation is when you typically see verbal memory deficits,” Brown explains.

Verbal Memory Outcomes are Different

But while this particular study did not establish a link between marijuana-induced sleep deprivation and impaired verbal memory, earlier research did find that long-term cannabis use is associated with poorer verbal memory in middle age.“Sleep
disruption from cannabis use isn’t necessarily insomnia-related or complete sleep deprivation; rather, it’s a reduction in the quality of sleep. Full sleep deprivation is when you typically see verbal memory deficits,” Brown explains.
The study published in the March 2016 edition of JAMA Internal Medicine, followed 3499 people over a 25-year-period, starting in early adulthood. At year 25, participants were assessed for both marijuana exposure and cognitive function.
Just over 84% of subjects reported using marijuana in the past, but less than 12% continued to use the drug into middle age.
This fact is important, because past marijuana use in early adulthood was associated with worsened verbal memory. For every 5 years of cannabis use, participants would fail to recall an average of one word from a list of 15.
In other words, the longer a person smoked pot, the worse their verbal memory later in life.  Furthermore, they tended to forget more words.

Young People Are Most at Risk

Dr. Francesca Filbey, PhD, a Professor of Psychology directs the laboratory where the UT Dallas study was conducted.  She is particularly concerned about how users younger than 25 may suffer disproportionate harm to sleep and brain connectivity.
And because the human brain continues to develop and mature until at least the mid-20s, the changes may be irreversible.
“Acute cannabis use affects many things, including sleep and working memory, and the field is undecided on whether those memory issues resolve after continued abstinence. When use begins in adolescence, sleep deficits are usually much more pronounced.“
“People who become dependent on cannabis for sleep risk developing tolerance and requiring greater doses for the same effect. People need to be aware of this,” Dr. Filbey says.

Dr. Philbey supervises the research of UT graduate student Tracy Brown.  The complete text can be read here: https://www.tandfonline.com/doi/full/10.1080/00952990.2024.2362832