Cannabis and cannabinoid-based products are increasingly consumed by a wide demographic for the purpose of improving sleep conditions such as insomnia. Sleep disorders are thought to affect at least 20% of the population, however, figures suggest that up to a third of people in the UK may suffer from chronic insomnia. Sleep problems is quickly becoming one of the most commonly reported reasons for using both medical and recreational cannabis and cannabinoid products.
A survey of adults visiting cannabis dispensaries in the US found that 74% of participants reported using cannabis to improve sleep. Of this group, 84% also reported that using cannabis had helped them to reduce or discontinue their sleep medication. Further, an international survey, completed by 953 participants from 31 countries, also indicated that sleep disorders were among the top five conditions for which they used medical cannabis.
A large number of studies and trials have assessed the effects of cannabis-based products in impaired sleep. Two systematic reviews have analysed the results from these studies, however, neither review conducted meta-analysis to pool effect estimates or evaluated the certainty of evidence. Further, the literature search of one of these reviews has become outdated.
A more recent systematic review, therefore, aimed to assess the existing evidence of the potential of medical cannabis and cannabinoids in the treatment of impaired sleep and to address the limitations of past reviews.
Studies included in the review
The researchers searched for eligible studies using MEDLINE, EMBASE, CENTRAL, and PsychINFO databases from inception to January 19, 2021. The reference lists of systematic reviews and all included studies were also reviewed to identify additional eligible studies.
Studies were considered eligible if they were randomised controlled trials (RCTs) and if they 1) enrolled patients aged 18 or over with impaired sleep; 2) randomised them to any form of medical cannabis or cannabinoid vs. a non-cannabis control; 3) collected outcome data at least 14 days after treatment.
Trials that included open-label treatments, trials that enrolled individuals using cannabis for recreational purposes, and studies exploring treatment for cannabis use disorder or cannabis withdrawal, were excluded from the review.
Findings of the review
A total of 136 articles were reviewed in full text and 38 publications reporting 39 RCTs with 5,100 enrolled patients, met the eligibility criteria.
While included studies used a number of instruments were used to measure sleep quality and sleep disturbance, the most commonly reported measure was the 10cm visual analogue scale (VAS). Therefore, researchers converted other measures to a 10cm VAS, as long as they had at least four categories of response options.
Sleep Quality
Evidence from 16 RCTs suggests that, compared to placebo, medical cannabis and cannabinoids result in a small increase in the number of patients that experience an improvement in sleep quality at or above the MID (the smallest amount of improvement that patients recognise as important). Similarly, four more studies that did not report data suitable for pooling also found that medical cannabis significantly improved sleep quality, in comparison to placebo.
Sleep Disturbance
The researchers also identified that the use of cannabinoids was associated with a small increase in the number of patients that reported less disturbance to sleep, compared with placebo.
Furthermore, high certainty evidence of people living with chronic non-cancer pain showed that, compared with placebo, cannabinoids increased the proportion of patients who experienced reduced sleep disturbance. Moderate certainty evidence collected from 5 RCTs of people living with chronic cancer pain found that medical cannabis results in a very small improvement in sleep disturbance, in comparison to placebo.
Other sleep-related outcomes
The researchers also found evidence from one included study that suggests that nabilone (a synthetic cannabinoid similar to THC) may reduce the frequency and intensity of nightmares in patients with PTSD. However, no significant benefits were identified for total sleep time or number of awakenings in the night.
Medical cannabis vs. Active comparators
There is evidence to suggest that nabilone may provide greater improvement in symptoms of insomnia as well as being associated with a slightly more restful sleep, compared with amitriptyline.
Conclusions
Having assessed the evidence from 39 randomised controlled trials, the authors of this systemic review conclude that there is moderate to high certainty evidence that, compared to placebo, medical cannabis or cannabinoids result in small improvements in sleep quality among patients with chronic cancer and non-cancer pain, and small and very small improvements in sleep disturbance in patients with chronic non-cancer pain and patients with chronic cancer pain, respectively.
This systematic review is the first in this area to statistically pool treatment effects of medical cannabis and cannabinoids on impaired sleep. However, the researchers concede that there are some limitations to the current research.
These limitations include the fact that most evidence identified was for non-inhaled cannabinoids in patients with chronic pain, meaning that these findings may not be generalisable to smoked or vapourised forms of cannabis in patients with other conditions. Furthermore, researchers were unable to explore the association between dose and effect estimates as most trials (28 of 39) allowed for post-randomisation titration by patients. Eligible trials also did not report on concurrent use of other medications that may interact with medical cannabis and cannabinoids.
