You have probably heard someone swear that a little cannabis helps them drift off at night. Maybe you have tried it yourself. For many people, it feels like a reliable way to switch the day off.
A new study in JAMA Network Open followed more than a thousand American adults for nearly 35 years. Even when cannabis users said their sleep felt fine, the wrist monitors on their arms told another story. Their sleep was less efficient and more broken up at night.
The researchers at Northwestern University drew on the long-running CARDIA heart study, following participants from their twenties into their sixties. The results were published in October 2026.
What the wrist monitors picked up
For one week, 891 participants wore an Actiwatch Spectrum sleep tracker on the wrist. The device recorded how much of the night they spent actually asleep, how fragmented their sleep was, and how long they lay awake after first dozing off.
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People who had used cannabis in the past month spent a smaller share of the night asleep than those who never used it. They were also more than three times as likely to have long stretches of being awake after first falling asleep.
The longer a person had used cannabis across their life, the stronger the pattern. Each extra year of cumulative use was linked to slightly less time asleep and more broken sleep.
Users felt no difference in their own sleep
When the same participants were asked how well they slept, the answers did not match the data. Cannabis users rated their sleep about the same as non-users on standard questionnaires.
The disruption showed up in the numbers but did not reach the people living with it. That gap is the central finding.
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"This study challenges the common belief that cannabis helps people sleep better," said Dr. Thanh-Huyen T. Vu, who led the work at Northwestern's Feinberg School of Medicine.
"Our findings suggest cannabis may actually be associated with poorer sleep quality, even if people don't perceive those changes."
This was an observational study not a controlled trial
The research tracked what people did and what their sleep looked like, but it did not test cannabis against a placebo. So it can show links, not causes.
People who already have poor sleep may also be more likely to reach for cannabis in the first place, which can muddy the direction of the link.
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The researchers also note that recent cannabis users were more likely to sleep longer than eight hours a night. More time in bed is not the same as better rest, and the study points out that longer sleep is not automatically healthier sleep.
How many people use cannabis for sleep
In 2024, CDC data showed about 3.7 percent of US adults used marijuana or CBD products most days or every day to help them fall or stay asleep. The share was highest among adults aged 18 to 34, at 5.5 percent, and fell to 1.7 percent in those 65 and older.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.