For a growing number of people, catching Zzz’s has become a joint effort.
Across the country, an estimated 22 million adults use some form of weed as a sleep aid, while another 45 million have tried it in hopes of getting more shut-eye, according to the National Sleep Foundation.
The bedtime ritual has plenty of believers: Roughly two-thirds of Americans who use the drug say it helps them get better rest.
But behind closed eyes, the story of what happens to the brain on cannabis is far more complicated — and scientists are still figuring out whether weed is improving sleep or simply reshaping it.
THC, the chemical largely responsible for marijuana’s high, works on the body’s endocannabinoid system — a complex cell-signaling network involved in regulating functions like sleep, mood and memory.
By activating cannabinoid receptors in the brain, it can have a calming effect that helps some people fall asleep faster.
CBD, another major compound in cannabis, doesn’t have the same psychoactive effects — but some research suggests it may indirectly help certain people rest by calming anxiety or easing pain.
The catch: Falling asleep faster is not necessarily the same as sleeping better, with some research suggesting quality takes a hit.
REM, interrupted
A 2025 review found that weed does not consistently improve sleep duration or how rested people feel. Other research suggests that chronic daily users spend more time awake during the night and experience poorer sleep quality compared with nonusers.
The reason may lie in the way the drug changes the brain’s carefully timed sleep cycle.
Throughout the night, the brain cycles between lighter sleep, deep slow-wave sleep — the most physically restorative stage — and REM sleep, the stage most closely associated with vivid dreams and believed to play an important role in memory consolidation, learning and emotional regulation.
Research suggests THC can decrease REM sleep. That may explain why many people who use it report dreaming less or not remembering their dreams after waking.
For some people, that can feel like a benefit.
In 2015, researchers found that a synthetic form of THC reduced nightmares for returning soldiers with treatment-resistant PTSD — suggesting that altering REM sleep could have therapeutic effects in certain cases.
California sober dreamin’
But weed’s effects on REM sleep may also have stranger consequences. Reports of unusually vivid or bizarre dreams are “very well known” in cannabis and neuroscience research, according to Andrew Kesner, assistant professor of psychology at Indiana University in Indianapolis.
“We know if you wake someone up in REM sleep, that’s when they have the highest chance to remember their dreams,” Kesner told Popular Science.
Researchers also suspect THC may influence the content of dreams themselves by altering activity in the cortex, the outer layer of the brain involved in processing information.
“It’s possible that the THC could be making dreams more intense by changing cortical activity, making them wonkier and maybe adding some variability to what you’re dreaming about,” Kesner explained.
But the effects of changing REM sleep may extend beyond dreams. Scientists believe the stage plays an important role in processing emotions, strengthening memories and organizing information gathered throughout the day.
Reducing the amount of time the brain spends in REM could potentially affect those functions, though researchers are still working to understand the long-term consequences.
“Memory has been widely known to be a potential impairment as a result of cannabis use, but we don’t know yet what the mechanisms are,” Dr. Francesca Filbey, director of the Cognitive Neuroscience Laboratory of Addictive Disorders, said in a press release. “We especially don’t know how that relates to people who use cannabis as a sleep aid.”
Doobie dependent
The brain may also begin adapting when THC becomes a regular part of the nightly routine.
With repeated exposure, the cannabinoid receptors that THC targets can become less sensitive, meaning the same dose that once helped someone drift off may eventually lose some of its effect.
As tolerance builds, some users may turn to more frequent use or higher-potency products to chase the same results — a pattern researchers have linked to worsening sleep outcomes over time.
“In terms of how cannabis influences sleep, very acute limited use has shown to help sleep, but when we see heavy chronic use, daily use, it’s associated with a host of sleep deficits, including insomnia, lower sleep duration, sleep-quality issues and longer sleep onset latency,” Evan Winiger, a researcher who has studied the topic at the University of Colorado Anschutz, said in a press release.
Those changes don’t immediately disappear when someone stops using cannabis. As the brain adjusts to functioning without regular THC exposure, the sleep system can temporarily fall out of balance.
Many people experience insomnia at first, followed by a surge of intense and sometimes disturbing dreams known as “REM rebound.”
Researchers believe this happens because the brain, after spending weeks, months or years with reduced REM sleep, attempts to compensate by increasing the amount and intensity of dreaming.
For some former users, those vivid dreams can become so distressing that they return to cannabis for relief.
“I have talked to people in recovery who have really violent nightmares, and that’s a factor for relapse,” Matthew Hill, a neuroscientist at the University of Calgary who studies the intersection of cannabinoids, stress and sleep, told the Washington Post. “I think the impact on sleep is considerable and scales up with potency.”
