Science

Cannabis worsens sleep quality measured on the wrist

Northwestern study of 1 266 adults tracked over 35 years finds users sleep worse than their own reports admit, daily weed use has already overtaken daily drinking in America

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A Northwestern Medicine study of 1,266 participants tracked from young adulthood into middle age found that both lifetime and recent cannabis users had objectively worse sleep than non-users — while reporting no such thing. Over nearly 35 years, researchers followed participants' cannabis use, then had them wear a wrist sleep monitor for a week in middle age and fill out surveys about their sleep quality. The study design let researchers compare what the monitor recorded against what the sleeper believed.

The gap was consistent. Greater lifetime marijuana exposure predicted worse objective sleep quality even after controlling for age, race, sex, smoking frequency, alcohol consumption and physical activity. Higher cannabis use over time correlated with being asleep for a lower percentage of the night and more sleep disruption. Recent users showed more fragmentation and lower sleep efficiency than people who never touched the substance — and were far more likely to sleep longer than eight hours a night.

"Our data do not support the belief that cannabis is helpful as a sleep aid," senior author Mercedes R. Carnethon said. A board-certified emergency physician not involved in the study put the finding plainly: participants who used cannabis demonstrated objectively poorer sleep, yet their own assessments of sleep quality did not reflect the difference. Someone may believe marijuana is helping them sleep while the measurements say otherwise.

The study could not distinguish modes of consumption — smoking versus edibles — and its authors call for more research on long-term effects. A related Fox News report notes America has passed a milestone of its own: daily cannabis use has now surpassed daily drinking.

The monitors were on the wrist while the users were sure it was working.