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The Sleep Whisperer is a series of columns offering insights and advice about sleep health. It is not a substitute for seeking professional medical care.

For many Canadians, cannabis has quietly become part of the nightly routine. Not for recreation, but for sleep.

In a national sleep survey of over 4,000 respondents, my research team showed that 15.6 per cent of Canadian adults were using cannabis specifically to help with their sleep. That represents more than half of those struggling with sleep problems. To put this in perspective, this slightly exceeds the 14.7 per cent of respondents who said they were using prescription sleep medications. While younger males were more likely to turn to cannabis for sleep, this practice cut across age groups and sexes.

Clearly, many people believe cannabis helps their sleep, but does it? To date, scientific evidence supporting cannabis as a sleep treatment remains inconsistent and insufficient. Yet some people feel cannabis helps them fall asleep or sleep more soundly. One leading hypothesis explaining the potential sleep-promoting effects of cannabis involves adenosine, a naturally occurring chemical that builds up in the brain across the day and helps promote sleep by dampening arousal in the brain. Cannabis appears to increase adenosine signalling – the opposite of caffeine, which keeps us awake by blocking it. Cannabis also interacts with the brain’s endocannabinoid system, which plays a role in regulating stress and sleep. These mechanisms offer a plausible explanation for why some people are using cannabis products at bedtime.

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Plausible, however, does not mean proven. While some studies report subjective improvements in sleep following THC or CBD use, others show no benefit. Research with objective laboratory sleep studies paint an equally mixed picture: cannabis has been shown to shorten or lengthen the time it takes to fall asleep, to reduce nighttime awakenings, to increase total sleep time, to increase both light and deep sleep, and to either suppress or increase REM sleep. Yet, many of these findings are based on just one or a few days of cannabis intake.

We know even less about the long-term effects of cannabis use on sleep. One question is about the possible build-up of tolerance. While more research is needed to confirm this, some of the sleep-promoting effects of cannabis could possibly diminish with repeated use. When one ceases to use cannabis, sleep can worsen temporarily – sometimes beyond baseline levels. In fact, among people who discontinue cannabis, sleep disturbance is one of the most commonly reported and distressing withdrawal symptoms, and a frequent reason for resuming use. This creates the risk of a familiar cycle: diminishing benefits over time paired with difficulty stopping, not unlike what occurs with certain prescription sleep medications. Which cannabis products, doses or patterns of use could fuel this cycle remains poorly understood.

Adding to the complexity is the cannabis plant itself. THC and CBD, its two most well-known compounds, can have markedly different – and sometimes opposing – effects on alertness and sleep. For instance, low doses of CBD may be stimulating, while higher doses may be sedating. What’s more, THC may modify the effects of CBD and vice-versa, and both are further influenced by other compounds found in cannabis plants, such as terpenes. With more than 500 chemical compounds inside cannabis and countless possible combinations, identifying the optimal sleep-promoting formulation is anything but straightforward.

Individual differences inherent to the person using cannabis may further muddy the waters. Responses to cannabis vary widely depending on genetics, age, sex, hormonal status and medical history. Hence, a person-centered approach may be critical to optimizing the effects of cannabis on sleep.

Scientists have started mapping specific conditions where cannabis may hold more promise. Emerging evidence notably suggests benefits for sleep in people with chronic pain, restless legs syndrome and post-traumatic stress disorder (PTSD).

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Sleep disturbance is a core feature of PTSD, often marked by vivid nightmares and an overactive REM sleep system. Poor sleep, in turn, interferes with PTSD recovery. A small but influential Canadian study in military veterans with PTSD showed that nabilone, a synthetic cannabinoid, significantly reduced nightmares and improved overall well-being. Nevertheless, in the absence of clear clinical guidelines, many veterans have relied on trial and error, often supporting each other and sharing hard-earned experiential knowledge through peer networks.

In my ongoing research with veterans living with PTSD, I have observed that those using medical cannabis tend to rely less on prescription sleep medications, antidepressants, opioids and antipsychotics than those who do not. Many confided this is because they experience more benefits and fewer side effects with cannabis. These findings are preliminary and require careful interpretation, but they underscore the need for more work in this area.

Eight years after non-medical cannabis was legalized in Canada, it has become widely available – and many people are using it to help with sleep. Yet, personal experience, no matter how compelling, cannot replace placebo-controlled clinical trials, just like we do for any other medical treatment. We urgently need robust research to determine whether cannabis works as a sleep aid, for whom, at what dose, in what formulation and for how long. Until then, cannabis will remain what it is today for many Canadians seeking better sleep: a hopeful and largely unguided experiment.

Dr. Rébecca Robillard, PhD, is a clinical neuropsychologist and associate professor at the School of Psychology at the University of Ottawa. She also leads clinical sleep research at The Royal mental health hospital. Robillard’s main area of work focuses on interactions between mental health, the sleeping brain and the sleeping heart. She co-chairs the Canadian Sleep Research Consortium, a national hub of sleep scientists and clinicians.