Photo : “it was 3 a.m.”/Flickr

We’ve written quite a lot lately about the potential benefits of marijuana (and there are quite a lot), but we shouldn’t idealize it and ignore the downsides: a recent study has shown that marijuana use is associated with impaired sleep quality.

It’s not the first time marijuana has been associated with lack of sleep quality. In the 1970s, two studies were published, analyzing the effects of THC on sleep patterns and on electroencephalographic sleep patterns, and concluded the same thing. The topic has seen a resurgence in recent years, with the discussion about marijuana legalization, and in 2008, the effects of several drugs on sleep were analyzed. If anything, this study confirms those studies, and at this point, it’s fairly safe to say that we’ve reached a consensus on this matter: long term consumption of marijuana is bad for your sleep.

This study shows that marijuana consumers take longer to fall asleep, struggle to maintain sleep, experience  non-restorative sleep and feel day time sleepiness. As expected, the strongest association was found in those who started consuming marijuana before 15. They were about twice as likely than the average to have severe problems falling asleep (odds ratio: 2.28), experienced non-restorative slee (OR: 2.25) and felt overly sleeping during the day (OR: 1.99). In those who started consumption after 15, the same trends were observed, but their effect was diminished.

“Current and past marijuana users are more likely to experience sleep problems,” said lead author Jilesh Chheda, research assistant at the University of Pennsylvania in Philadelphia, working with Dr. Michael Grandner, the senior author on the study. “The most surprising finding was that there was a strong relationship with age of first use, no matter how often people were currently using marijuana. People who started using early were more likely to have sleep problems as an adult.”

The study was conducted on people who answered the 2007-2008 National Health and Nutrition Examination Survey (NHANES). Out of them, 1,811 participants reported a drug history. It’s important to note that this study doesn’t tackle the issue of causality – as we discussed previously, it’s important to note that just because things are associated, it doesn’t necessarily mean that one is causing the other. It seems fairly easy to infer that marijuana would be causing the sleep disorders, but that would be a leap – and a scientifically incorrect one at that. Perhaps people with sleep disorders are more inclined to start using marijuana, or perhaps it’s a coincidence, or some other factor we haven’t taken to account. It’s about time we started to understand the effects of the drug on the human body.

“Marijuana use is common, with about half of adults having reported using it at some point in their life,” said Chheda. “As it becomes legal in many states, it will be important to understand the impact of marijuana use on public health, as its impact on sleep in the ‘real world’ is not well known.”