Can Cannabis Really Help You Sleep? A New Study Says Not So Fast
Many people use cannabis at night as a sleep aid, hoping it will help them fall asleep faster or stay asleep longer. But judging whether it works is trickier than it sounds. Someone can wake up several times in the night and still get up in the morning feeling they slept fine. That seems to be what happened for many cannabis users in a new study.
Dr. Thanh-Huyen T. Vu, a research associate professor of preventive medicine at Northwestern University Feinberg School of Medicine, was the corresponding author. Her team didn't give anyone cannabis. They looked for patterns in a long-running group of adults, so the results show a link rather than proof that cannabis caused the poorer sleep.
"This study challenges the common belief that cannabis helps people sleep better," Vu said. "Our findings suggest cannabis may actually be associated with poorer sleep quality, even if people don't perceive those changes."
Following Cannabis Use for Decades
Earlier studies of cannabis and sleep were often short-term or depended on people describing their own sleep. Vu's team could go much further back. Their cannabis records covered decades.
The records came from the Coronary Artery Risk Development in Young Adults (CARDIA) study. It started in 1985 and 1986 with 5,115 Black and White adults aged 18 to 30. For the new analysis, the researchers kept the 1,266 participants who had enough information on both cannabis use and sleep.
Their cannabis use had been recorded over and over, from young adulthood into middle age. Every bit of that use was then added up in cannabis-years. One cannabis-year is 365 days of use in total, and those days can be spread across several years. The team also split people by how recently they had used cannabis: some had never tried it, some had used it in the past, and recent users had used it within the previous 30 days.
In middle age, 891 of the participants wore an Actiwatch Spectrum PLUS on the wrist for a week. The researchers used its record of their movements to estimate how each night went.
Heavier Use Linked to Restless Sleep
The watch gave the team four measures: total sleep time, the share of the sleep period spent asleep, restlessness, and time awake after first falling asleep. Time awake after falling asleep is the one most people will recognize. Eight hours in bed can include a lot of waking up, and those hours don't count as solid sleep.
Age, sex, race, cigarette smoking, alcohol use, physical activity, depression, chronic health conditions, sleep medication and other drug use can all affect sleep. The researchers adjusted for each of them, and greater lifetime cannabis use was still linked to more disrupted sleep.
- With each additional cannabis-year, the share of the sleep period spent asleep was 0.18 percentage points lower.
- Restlessness was 0.20 percentage points higher.
- People spent about 0.85 more minutes awake after first falling asleep.
Lifetime use wasn't linked to how many hours people slept. It was linked to how settled and continuous those hours were.
Recent Users Slept Longer, But With More Interruptions
Recent users slept about 20 minutes longer on average than people who had never used cannabis. On its own, that looks like a point in cannabis's favor. But other measurements revealed more disrupted sleep.
Recent users spent a smaller share of the sleep period asleep, their sleep was more fragmented, and they were awake for about 11 extra minutes after first falling asleep. Their odds of lying awake for at least 30 minutes after sleep began were more than three times higher, too. Longer nights, for this group, came with more interruptions.
Mercedes R. Carnethon, chair of the Department of Preventive Medicine at Feinberg, is the study's senior author. "Our data do not support the belief that cannabis is helpful as a sleep aid," Carnethon said. "As cannabis becomes increasingly available and accepted, it's important to better understand its long-term associations with health behaviors such as sleep."
People Did Not Feel Worse
Participants also rated their own sleep on the Pittsburgh Sleep Quality Index (PSQI), a questionnaire about how well people think they sleep. Cannabis users didn't score any worse on it, even though their watches had recorded more broken sleep.
"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."
That gap may be part of the reason cannabis keeps its reputation at bedtime. Someone who sleeps a little longer may not notice waking up later in the night.
Simple Sleep Habits Still Matter
Study co-author Kristen L. Knutson is an associate professor of neurology at Feinberg who studies sleep medicine. She recommended several simple habits for better sleep:
- Keep a regular bedtime.
- Make your bedroom cool, dark and quiet.
- Avoid looking at phones and other screens right before bed.
- 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.
Important Questions Remain
The watches measured sleep for one week in middle age. Nobody's sleep was tracked alongside their cannabis use across all 35 years, so the researchers can't say how the two changed together over time.
Cannabis use was self-reported. The team didn't know how strong the products were, how much THC or CBD they contained, or how close to bedtime people used them. Smoking and eating cannabis weren't separated either. Two people with the same number of cannabis-years could have used it in very different ways, and their habits probably shifted over the decades. The authors said how people use cannabis is an especially important question for future studies.
The full study was published in the journal JAMA Network Open.
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