Many insomniacs swear by cannabis as a way to help them sleep – while many scientific studies have found that THC actually exacerbates sleep problems.
A new study published last week in Addiction might explain why.
Researchers from the University of Southern California’s Keck School of Medicine found that for young adults with pre-existing depression or anxiety, cannabis improved sleep. For those without pre-existing mental health conditions, it created more sleep problems.
“There’s a common perception that cannabis can improve sleep, but the science on cannabis’s effects on sleep is mixed, and part of the reason could be because individual factors like mental health play a role in how cannabis use affects sleep,” says Claire Walsh, a PhD student in behavioral health at USC and lead author of the study.
Walsh and her team used data from USC’s Happiness and Health Study, which surveyed 3,300 public high school students in the Los Angeles area on their substance use, social and emotional health, as well as other health factors, between 2013 and 2023.
The study compared people who use cannabis 20 or more days each month with those who have never tried it, and determined how cannabis affects sleep problems using a 16-point scoring system. Walsh says that for participants who were anxious or depressed, her team saw “an average decrease in sleep problems of -1.18 points over six months”, and for participants without anxiety or depression, they saw “an average increase in sleep problems of 1.66 points over six months” compared with those who didn’t use cannabis.
Walsh isn’t sure why cannabis affected people with anxiety or depression differently. One possibility is that THC helps mask the symptoms of anxiety or depression, which can have a negative impact on sleep.
“However, this doesn’t necessarily mean cannabis is treating the underlying mental health condition,” she emphasized.
Research shows that people who use cannabis are more likely to have anxiety and depression, and evidence is mixed on whether or not the cannabis is helping.
“Sleep is regulated by the endocannabinoid system, and that cannabis tickles the endocannabinoid system, and that even though we don’t know the exact pathway, we know that the endocannabinoid system mediates sleep,” says Peter Grinspoon, a physician and Harvard Medical School instructor who wrote Seeing Through the Smoke, about medical cannabis.
Grinspoon says that people with anxiety or depression might find cannabis more beneficial for sleep because they’re more likely to struggle with insomnia in the first place.
“It’s easier to help someone who has a problem than someone who doesn’t,” he said. Another possible explanation for the varying effects could be that people use cannabis differently if they’re trying to sleep rather than get high.
The USC study investigated how frequently people use cannabis containing THC, but not the size of their dose or their method of consumption. Grinspoon says that people who consume cannabis with the specific intention of improving their sleep quality likely use lower doses because high doses can be stimulating and keep people awake.
Grinspoon suspects that much of the scientific research showing cannabis hurts sleep quality is using skewed methodologies.
“A lot of the cannabis research has been done under the auspices of the ‘war on drugs’, and there’s been a huge, major emphasis on finding harms and very little emphasis on finding benefits,” he said.
Restrictions on cannabis research also prevent most researchers from studying cannabis in a lab setting, which means they must rely on real world data about whatever cannabis participants happen to be using.
“We’ve been studying illegal cannabis, God knows what’s in it. That’s like studying moonshine to try to understand alcohol. And then we’ve been studying smoked cannabis, which is the least healthy way to take it,” Grinspoon added.
Much of the more recent, specifically targeted research on cannabis and sleep shows promise.
For example, a study from earlier this year looked at patients in the UK who treated their post-traumatic stress disorder (PTSD) with vaporized cannabis of the Hindu Kush strain. The researchers chose Hindu Kush because it’s “a well-established cannabis strain with a stable genetic background and a well-characterized chemical and pharmacological profile”. The study found that participants experienced significant sleep improvements over a period of six months.
Even when cannabis does help people sleep, it still comes with risks.
Like other sleep medications, cannabis carries a risk of dependence, and people who decide to quit might experience withdrawal symptoms, including even worse insomnia. Researchers have also raised concern over the fact that cannabis can reduce the amount of time people spend in rapid eye movement (REM) sleep, which means they’ll have fewer dreams.
“Hypothetically, that could be a problem,” says Grinspoon, adding that we still don’t understand sleep well enough to know the implications of missed REM sleep.
But, he says, other popular sleep aid medications like trazodone, Ambien and Benadryl also reduce REM sleep, so “it’s kind of this double standard for cannabis, as usual”.
