Think cannabis helps you sleep better? Think again.

• Study followed adults for 35 years, from young adulthood into middle age
• Long-term cannabis use linked to lower sleep quality measured by wrist-worn monitors
• Findings suggest cannabis-related sleep disruptions may go unnoticed by users themselves
• Sleep medicine expert offers well-established strategies that can improve sleep quality

CHICAGO — Millions of Americans use cannabis products as sleep aids, but a new Northwestern Medicine study suggests marijuana may not improve sleep the way many people believe it does.

The study found both lifetime and recent cannabis use were associated with poorer objectively measured sleep quality, even though participants generally did not perceive their sleep to be worse.

The scientists followed participants from young adulthood into middle age for nearly 35 years, repeatedly tracking their cannabis use over time. In middle age, participants wore a wrist-based sleep monitor for a week and completed sleep surveys, allowing the scientists to compare objective measures of sleep with participants' own perceptions of how well they slept.

The study found both long-term and recent cannabis use were associated with poorer sleep quality when the wrist-worn monitoring device objectively measured participants’ sleep. However, participants who used cannabis generally did not report sleeping worse than people who didn't use it. The findings suggest cannabis-related sleep disruptions may go unnoticed by users themselves, the study authors said.

The study was published Oct. 9 in JAMA Network Open. 

“This study challenges the common belief that cannabis helps people sleep better,” said corresponding author Dr. Thanh-Huyen T. Vu, research associate professor of preventive medicine (epidemiology) at Northwestern University Feinberg School of Medicine. “Our findings suggest cannabis may actually be associated with poorer sleep quality, even if people don't perceive those changes.”

While the study was not designed to determine whether cannabis directly causes sleep problems, it provides some of the strongest evidence to date that long-term recreational cannabis use and better sleep quality may not be as closely aligned as commonly believed.

“Our data do not support the belief that cannabis is helpful as a sleep aid,” said senior author Mercedes R. Carnethon, chair of the department of preventive medicine at Feinberg. “As cannabis becomes increasingly available and accepted, it's important to better understand its long-term associations with health behaviors such as sleep.”

A breakdown of the study findings

The study analyzed data from the Coronary Artery Risk Development in Young Adults (CARDIA) Study, a long-running, community-based study that began in 1985-86 and follows Black and white adults across the U.S.

Among 1,266 participants, the study found greater lifetime cannabis exposure was associated with poorer objective sleep quality. People with higher cumulative cannabis use spent a lower percentage of the night asleep, experienced more fragmented sleep and spent more time awake after initially falling asleep.

Recent cannabis users showed similar patterns. Compared with people who never used cannabis, recent users were more likely to have lower sleep efficiency, greater sleep fragmentation and longer periods of wakefulness during the night. They also were significantly more likely to sleep longer than eight hours per night, the study found.

When researchers asked study participants to rate their own sleep quality, however, cannabis use showed no association with whether people felt they slept well or poorly.

“This was one of the most interesting findings,” Vu said. “The wearable device detected more nighttime disruption among participants with long-term cannabis exposure, but the participants themselves generally did not report worse sleep.”

After adjusting for numerous factors known to affect sleep — age, sex, race, cigarette smoking, alcohol use, physical activity, depression, chronic health conditions and use of other substances — cannabis use remained associated with poorer objectively measured sleep, the study found.

The researchers did not distinguish between modes of cannabis consumption (e.g., smoking versus consuming edibles). Given that the participants were followed over several decades, patterns of cannabis use likely changed over time, which the study authors said makes this an especially important question for future studies.

Better ways to support healthy sleep

While cannabis may not be the sleep solution many people believe it is, there are well-established strategies that can improve sleep quality, said study co-author Kristen L. Knutson, associate professor of neurology (sleep medicine) and preventive medicine (epidemiology) at Feinberg.

“Keep a regular bedtime, make your bedroom cool, dark and quiet, and avoid looking at phones and other screens right before bed,” Knutson said. “It can also help to establish a calming routine before sleep, such as reading, meditating or taking a shower. If sleep problems persist, or if you're a loud snorer, talk with your health care provider to rule out an underlying sleep disorder.”

The study is titled, “Recent and Cumulative Cannabis Use and Sleep in Middle-Aged Adults.” The CARDIA study is supported by the National Heart, Lung, and Blood Institute (NHLBI) in collaboration with the University of Alabama at Birmingham (grants 75N92023D00002 and 75N92023D00005), Northwestern University (grant 75N92023D00004), University of Minnesota (grant75N92023D00006), and Kaiser Foundation Research Institute (grant75N92023D00003). The CARDIA Sleep Ancillary Study is funded by grant R01HL152442 from the NHLBI.