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Larry Mitchell never thought much about the dreams he wasn't having.
For years, while he regularly smoked cannabis, his dreams seemed to disappear. Then, last summer, he quit. Soon afterward, his nights became populated by a vivid nocturnal world unlike anything he had experienced before.
There was the dream in which he was driving his old green 1985 Lincoln - with its white leather seats - alongside his dead cousin, listening to C-Bo. Another found him sitting on the steps outside a club talking with friends. And then there were the sex dreams.
They were so real and so electrifying, Mitchell said, "I was excited to go to sleep."
Mitchell, a 51-year-old from the manufacturing hub of Kokomo, Indiana, who spent years working as a chef before taking a factory job, had inadvertently found himself at the center of one of sleep science's enduring mysteries.
Cannabis alters consciousness in obvious ways while people are awake. Only recently have scientists begun to gain new understanding into how the drug reshapes dreaming, sleep architecture and the brain's overnight housekeeping - but many basic questions remain unresolved. Learning how cannabis influences sleep could help people weigh its potential short-term benefits against possible long-term effects on sleep quality and brain health.
Unlike a single medication with a fixed dose, cannabis comes in an enormous range of chemical profiles and products. More than 120 cannabinoids, different methods of consumption, ever-rising THC potency, and frequent use alongside tobacco or other drugs make it difficult to isolate what is driving any particular effect.
That complexity has slowed the science, even as cannabis has become one of the country's most widely used psychoactive substances.
Millions of Americans use cannabis, and for many, it has become part of a nightly ritual. But whether people reach for it as a sleep aid or for entirely different reasons, the drug doesn't stop working when they close their eyes.
Why do we sleep?
Sleep is often treated as a luxury rather than a necessity in the modern world. But science tells us that it's one of the most important determinants of human health. It's when the brain consolidates memory, clears metabolic waste and orchestrates countless other key physiological processes.
It is perhaps unsurprising, then, that so many people turn to cannabis in pursuit of a better night's sleep. A study published in June in Sleep Health, based on a nationally representative survey, estimated that roughly 9 percent of U.S. adults use cannabis as a sleep aid.
Scientists have been studying the relationship between cannabis and sleep for more than half a century. By the 1970s, researchers had begun investigating the plant's two best-known cannabinoids - tetrahydrocannabinol, known as THC, and cannabidiol, known as CBD - for their effects on sleep and wakefulness.
Early attention centered on THC, the primary psychoactive compound in cannabis producing its intoxicating effects. Because THC appeared to induce drowsiness and shorten the time it takes to fall asleep, it was initially explored as a potential sleep medication. But newer hypnotic drugs became available that offered similar benefits with fewer psychoactive side effects.
Subsequent research has revealed that different cannabinoids can have widely varying effects on sleep. In controlled laboratory studies, it looked like a dose of THC might help people fall asleep more quickly, but CBD showed little consistent evidence of directly promoting sleep. Its potential benefits appear to be indirect by reducing anxiety in some individuals.
"We know cannabis use is changing sleep. Whether it's for the good, as some people want to promote, or for the bad, we don't know," said Nicole Bowles, an associate professor at Oregon Health and Science University.
Bowles has been studying the subject for about 10 years, since she was a graduate student and marijuana became legalized for recreational use in Oregon. She runs a laboratory focused specifically on how THC influences sleep.
She said people who use cannabis have pretty consistently reported in studies that they get better sleep. But here's the catch: When scientists have attempted to measure sleep quality, nearly every study has shown it to be worse, including how often people wake up after falling asleep.
In one small study, Bowles attached monitors to nine people who had never tried marijuana and nine who regularly used cannabis and tracked their sleep. All were healthy with no major health concerns. The conclusion: Cannabis seemed to not help their sleep at all.
"There is a mismatch between what people feel the cannabis is doing and what we are seeing objectively," she said.
But helping people fall asleep is only part of the story. THC also appears to change what happens after sleep begins.
Disappearing dreams
Among the wildest anecdotal reports about cannabis use have to do with dreams. Many who are regular cannabis users report fewer dreams - or remember fewer of them.
Researchers have offered a compelling explanation: Laboratory studies suggest that THC suppresses rapid eye movement, or REM, sleep, the third major stage of the sleep cycle, which is believed to play a critical role in memory consolidation, emotional regulation and learning. Over the course of the night, the brain moves through a repeating sequence: from light sleep into deep, slow-wave sleep and then into REM sleep - the phase most closely associated with vivid, emotionally charged dreams. By reducing the time spent in REM, THC may also diminish the intensity and frequency of dreaming.
Some of the strongest clues came from clinicians treating patients whose dreams had become pathological.
A landmark 2015 double-blind, placebo-controlled study led by Rakesh Jetty, a Canadian military psychiatrist, looked at the effects of a synthetic analogue of THC on returning soldiers. They suffered from severe, treatment-resistant post-traumatic stress disorder.
The study showed that the right dose not only helped with hyperarousal during the day but also quieted the former soldiers' nightmares.
Ryan Vandrey, an experimental psychologist who helps run the Johns Hopkins Cannabis Science Laboratory, said THC exerts its effects by binding to the brain's cannabinoid receptors, which help maintain a balance between excitatory and inhibitory neural activity.
"The brain's endocannabinoid system is really a system that balances arousal," he said.
With chronic use, the brain adapts by reducing the number and sensitivity of these receptors. When THC use stops, the endocannabinoid system is temporarily unable to function normally, disrupting sleep regulation.
While the study was small, it suggested that manipulating the brain's endocannabinoid system appeared to change not just sleep but the content of dreams themselves.
REM rebound
Sleep, it turns out, may have a way of settling its debts. After weeks or months of suppressed dreaming, users in studies and throughout social media who stop cannabis have described how the brain compensates with an explosive return of an unusually emotional or bizarre REM rebound.
If dreams have a function, it may be to let the brain experiment safely. Some scientists have suggested it might serve as an "overnight workshop" that allows us to simulate threats, rehearse social encounters, strengthen memories, and process emotionally charged experiences before waking returns us to the real world.
Just how harmful is it to stop dreaming? Matthew Hill, a neuroscientist at the University of Calgary who studies the intersection of cannabinoids, stress and sleep, believes there are reasons to think the loss of dreaming is not entirely benign.
Some of the strongest evidence comes from people with cannabis use disorder, a medical condition marked by compulsive cannabis use. Hill said that disrupted sleep is among the most common and persistent symptoms these individuals experience.
Evidence linking occasional cannabis use to dementia is inconclusive for now, but a 2025 study of more than 6 million adults published in JAMA Neurology found that cannabis use that is severe enough to require hospitalization or emergency care is linked to a 72 percent higher risk of a new dementia diagnosis in the following five years.
One of the biggest challenges of quitting cannabis is what happens to sleep. When some people stop using it, they first experience insomnia, followed by a rebound in REM sleep that can trigger unusually vivid - or even terrifying - dreams. For some, those nightmares become so distressing that they drive a return to cannabis, creating a cycle in which the drug both suppresses dreaming and becomes the only reliable way to escape its rebound.
"I have talked to people in recovery who have really violent nightmares, and that's a factor for relapse," Hill said. "I think the impact on sleep is considerable and scales up with potency."
But the question of why we dream has never belonged to science alone. It encompasses neuroscience, philosophy and spirituality.
Mitchell's dreams have become less intense with time, but they still occur with regularity. He has no intention of using cannabis again, he said, because he does not want to lose the ability to dream once more.
Mitchell believes that dreaming fuels his creativity. He continues to experiment with vegan recipes (stuffed green tomatoes; jackfruit birria tacos), sharing them online, and enjoys creating and playing music. He said he has come to see cannabis as stifling his creativity. "Some people say it enhances it," he said. "I feel like it slows you down."
But even more important, dreaming connects him to those he has lost.
Years ago, his cousin - who was also his closest friend and roommate - died at 43 of cancer that had spread to his throat. Mitchell keeps his ashes at home. In dreams, however, their conversations continue.
"Having dreams is very important," he said. "They connect you to different timelines in life. They can give you hints and signs of the future, and they can give you closure."
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