An extra twenty minutes of sleep sounds like a decent deal. Until you find out you've spent more of the night waking up. That's roughly the puzzle researchers at Northwestern University ran into when they examined cannabis use and sleep. They had data stretching back decades, plus a week of wrist-monitor readings from 891 adults. And the numbers weren't quite what you might expect from something people often use to help them sleep.
Participants who had used cannabis in the previous month slept around twenty minutes longer than those who had never used it. But their sleep was also more broken up. They spent roughly eleven extra minutes awake after first falling asleep. The researchers found similar patterns when looking at years of cannabis use. Here's the odd bit: when participants rated their own sleep, those differences didn't really show up. Apparently, your wrist can keep a different account of the night than your memory does.
The study appeared in JAMA Network Open on October 9. Nobody was handed a joint and sent to bed for this experiment. Researchers analysed existing records and measured sleep during one week, so they can't say cannabis caused the differences. The participants were around sixty years old on average, too. That leaves plenty of questions about younger users. Still, it's an interesting finding for anyone who judges a night's sleep by how quickly their head hits the pillow.
