Sleep disorders are thought to affect a significant proportion of the human population, globally. In fact, it is believed that only around a third of people in the UK are classified as ‘good sleepers’. Sufficient sleep is vital to maintain regular function. Dysfunctional sleep can lead to irregular brain and bodily homeostasis, energy levels, and cognitive ability.

Cannabis has long been known to have significant therapeutic and medicinal potential and its effects on sleep can be traced back to reports in medical journals during the 1800s. Cannabinoids, which are found both within the cannabis plant (phytocannabinoids) and within our bodies (endocannabinoids) have the potential to promote normal sleep behaviour.

In a recently published review, researchers aimed to summarise the current evidence base concerning the interaction of cannabinoids, endocannabinoids, and sleep. For this review, researchers analysed previous studies that assessed the mechanisms of endocannabinoids and cannabinoids and how they influence sleep in both humans and rodents.

The Endocannabinoid System

Endocannabinoids are lipid-based metabolites that are involved in a number of neuromodulatory actions including mood, pain detection, and sleep. The two most well-recognised endocannabinoids are anandamide and 2-arachidonoly-glycerol (2-AG). These endogenous cannabinoids interact with cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2). Together, these receptors and cannabinoids make up the most recognised elements of the endocannabinoid system.

In aiming to manipulate the endocannabinoid system, treatments may be used to either enhance or diminish the concentration of endocannabinoids. For example, the administration of agents that increase the amount 2-AG or anandamide, or the administration of the cannabinoids themselves. On the other hand, other agents, such as compounds that may block the endocannabinoids from binding to endocannabinoid receptors, will decrease activity.

How do Endocannabinoids Influence Sleep?

It is not yet clear which endocannabinoid has the greatest effect on sleep modulation, and it is theorised that both anandamide and 2-AG may be involved in the process. Studies have found that increasing the levels of either of these endocannabinoids – through the inhibition of enzymes responsible for their catabolism – increased non-rapid eye movement (REM) sleep and regulated sleep stability in mice.

Cannabinoids and Sleep

While it is becoming increasingly apparent that endocannabinoids play a prominent role in sleep and sleep neurophysiology, more research is required to fully understand how cannabinoids may alter these processes. Various studies, in both humans and rodents, have demonstrated that the administration of cannabinoids, such as tetrahydrocannabinol (THC) and cannabidiol (CBD), may help to induce sleep and decrease the chance of waking after the onset of sleep.

The Effects of THC on Sleep

For example, a 2017 survey that assessed the responses of over 1,500 patients at a New England medical cannabis dispensary showed that around two-thirds decreased their use of pharmaceutical sleep aids in favour of medical cannabis.

In addition, a number of studies have indicated that chronic THC exposure, as well as other CB1-activating compounds, appears to improve sleep. However, many of these studies recognised as being of low quality. Additional evidence has also been collected which indicates that cannabis use may also provide relief to individuals who suffer from poor sleep as a result of post-traumatic stress disorder (PTSD) and pain.

On the other hand, other studies have suggested that while moderate use of cannabis may help to improve sleep, repeated exposure to cannabis and THC also produces tolerance to these actions of the drugs. This often means that patients will have to use more of the drug/compounds to experience the desired effect, and in some cases, this may cause withdrawal symptoms when the drug is removed. Furthermore, other studies have concluded that withdrawal may lead to sleep disruption in individuals following chronic cannabis use.

The Effects of CBD on Sleep

While most past studies on cannabinoids in sleep modulation have focused on THC, an increasing number of studies have begun to focus on the potential of CBD. However, results remain unclear on the overall effect that CBD may have on improving sleep. For example, one study found that CBD had opposing effects to THC when it came to sleep, appearing to have wake-enhancing effects as opposed to the sedative properties seen in THC administration.

On the other hand, some studies which used a self-report model among participants reported a modest improvement in sleep. Other evidence suggests that a near-equal administration of both THC and CBD may improve sleep without increasing a patient’s tolerance to the compounds. If proven, this may present an opportunity for cannabinoids to be used as a sustainable treatment for sleep disorders.

Conclusions

There have been many studies carried out over the past few decades that have delivered promising results for the use of cannabinoids to modulate sleep. However, the researchers of the prior mentioned review suggest that more large-scale clinical trials should be carried out in order to gain a clearer understanding of how these compounds could help to modulate sleep.