Millions of insomniacs turn to cannabis, swearing it lulls them into a much-needed rest. But science tells a different story — one that’s not quite so simple. For years, researchers have been divided on whether cannabis is a remedy or a culprit when it comes to sleep problems. Now, a new study may offer some much-needed clarity.

The new research suggests that the effects of cannabis on sleep may depend on a crucial factor: mental health. For young adults already struggling with anxiety or depression, cannabis seemed to improve sleep. But for those without such conditions, the drug had the opposite effect, worsening sleep quality.

“There’s a common perception that cannabis can improve sleep, but the science on cannabis’s effects on sleep is mixed, and part of the reason could be because individual factors like mental health play a role in how cannabis use affects sleep,” Claire Walsh, a PhD student in behavioral health at the University of Southern California and the lead author of the study told The Guardian.

Cannabis, Anxiety, and Sleep: A Complex Relationship

Researchers led by Walsh tapped into data from the USC Happiness and Health Study, which followed over 3,300 high school students in Los Angeles from 2013 to 2023. The team zeroed in on cannabis use, comparing regular users — those who used the drug 20 or more days a month — to those who had never tried it.

The findings were striking. Participants with anxiety or depression who used cannabis reported fewer sleep issues, with an average reduction of 1.18 points on a 16-point sleep disturbance scale over six months. Meanwhile, those without these mental health conditions saw their sleep problems worsen, with an average increase of 1.66 points.

But why would cannabis have such opposing effects? It’s unclear, and Walsh is cautious about jumping to conclusions. One theory is that THC, the primary psychoactive compound in cannabis, might temporarily mask the symptoms of anxiety or depression, indirectly improving sleep. However, she stresses, “this doesn’t necessarily mean cannabis is treating the underlying mental health condition.”

The endocannabinoid system consists of receptors scattered throughout the brain and body. These receptors help regulate a host of bodily functions, including mood, appetite, pain, and yes, sleep. When activated, they can influence how easily we fall asleep, how deeply we slumber, and how long we stay in the most restorative phases of sleep.

Cannabis, particularly its psychoactive component THC, taps directly into this system. THC binds to the same receptors as naturally produced endocannabinoids, triggering similar effects. Some studies suggest that low doses of THC might help people relax and drift off to sleep more easily by reducing the anxiety and racing thoughts that can keep us awake. But like a conductor waving the baton too forcefully, high doses can overstimulate these receptors, leading to restlessness and disrupted sleep cycles.

A Difficult Substance to Study

One of the challenges of cannabis research is the wide variability in how people use the drug. Walsh’s study focused on the frequency of cannabis use but did not account for dosage or consumption methods. But these things aren’t easy to control for when studying the effects of an illegal drug. Cannabis is still classed as a Schedule 1 drug in the U.S. at the federal level — the same class as cocaine and heroin.

But it’s not just dosage that complicates the picture. Many studies examining cannabis and sleep quality have been hampered by decades-long restrictions on cannabis research. A lot of the cannabis research — especially before the massive legalization wave in the U.S. — has been done under the auspices of the ‘war on drugs’. So, these studies are generally biased toward finding harmful effects with little emphasis on finding benefits.

Still, even if cannabis does help some people drift off, it’s not without its risks.

More Factors to Consider

Like other sleep aids, cannabis use can lead to dependence. Those who decide to quit may find themselves facing withdrawal symptoms, including insomnia even worse than before.

There are also concerns about how cannabis affects sleep architecture. Some studies suggest that cannabis reduces time spent in rapid eye movement (REM) sleep — the phase most associated with dreaming. This could potentially have unknown long-term effects on mental health and cognitive function.

“Hypothetically, that could be a problem,” says Grinspoon, a physician and Harvard Medical School instructor who wrote Seeing Through the Smoke, about medical cannabis. But he is quick to point out that other common sleep medications like trazodone and Ambien also reduce REM sleep. “It’s kind of this double standard for cannabis, as usual,” he told The Guardian.

In light of these recent findings, Grinspoon says that those looking to cannabis for sleep might use lower doses, as higher doses can be too stimulating and disrupt rest. In related news, a study from The University of Texas at Dallas found that long-term cannabis use can disrupt sleep, which in turn worsens memory, especially spatial memory, among heavy users.

Published in the American Journal of Drug and Alcohol Abuse, the study found that while cannabis use alone doesn’t directly impair memory, sleep disturbances in those with cannabis use disorder (CUD) can exacerbate cognitive decline. Researchers noted that cannabis disrupts slow-wave sleep, which is important for memory, particularly in younger users whose brains are still developing.

The findings appeared in the journal Addiction.