Just like drinking coffee to feel awake, many substances can affect the dynamics of our circadian cycle. Cannabinoids are assumed to enhance sleep due to the somnolence caused by certain doses, but can they improve sleep? The circadian cycle is a natural process that regulates the sleep–wake cycle every 24 hours. It is the result of complex systems including neurons and neurochemicals, synchronized with the master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus.
Sleep stage can be divided into REM (rapid eye movement) and NREM sleep. These are regulated, by GABAergic, cholinergic, and serotonergic neurons located in different brain areas that will induce both sleep stages. Those neuronal terminals also have CB1 receptors which will be activated by cannabinoids and consequently, can impact the SCN clock that follows light cues.
Some studies have shown that levels of endocannabinoids are very different during the “light phase” and the “dark phase” and can enhance the activation of the serotonergic system. Therefore, activation of CB1 receptors can be an outstanding approach to regulate the circadian cycle. This theory sounds scientifically logical, but current studies in cannabis users and lab animals are contradictory and not persistent. Short term studies have shown that acute exposure to cannabinoids can decrease sleep-onset latency, meaning that the consumer will fall asleep faster. Also, they can increase total sleep time and deep sleep (slow wave sleep). Conversely, some other studies showed a reduction of deep sleep and a decrease of REM sleep, not only with acute doses, but also, with chronic intakes of cannabinoids. Even though these outcomes are so conflicting, there are other studies suggesting cannabinoids can be used to decrease insomnia severity and others have proposed they can improve wakefulness.
Overall, most studies were tested with either cannabis or THC. There are a few cannabidiol (CBD) studies, with opposite results as well. The lack of uniformity in the outcomes of the existing studies may be due to the biphasic effect of cannabinoids, where low and high doses can exhibit completely opposite effects. Although the foregoing is just a theory, we should keep in mind that some studies are based on subjective measures, and long-term effects may be affected by the regular administered dose, periodicity of cannabinoids usage and the possibility of tolerance to these compounds.
Scientists have provided the foundation to study the effect of cannabinoids in the circadian cycle, and I am sure there will be consistent evidence in the future. By now, we must be aware that cannabinoids can impact the circadian cycle and its sleep stages, they may help relaxation by diminishing anxiety, but if you are trying to get better sleep, it is difficult to ascertain if cannabinoids are the answer.
Stay tuned – There is no greater ignorance than thinking you know it all.
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- Kaul, M., Zee, P. C., & Sahni, A. S. (2021). Effects of Cannabinoids on Sleep and their Therapeutic Potential for Sleep Disorders. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics, 18(1), 217–227. https://doi.org/10.1007/s13311-021-01013-w 
- Healy, K. L., Morris, A. R., & Liu, A. C. (2021). Circadian Synchrony: Sleep, Nutrition, and Physical Activity. Frontiers in network physiology, 1, 732243.
- Haj-Dahmane, S., & Shen, R. Y. (2011). Modulation of the serotonin system by endocannabinoid signaling. Neuropharmacology, 61(3), 414–420. https://doi.org/10.1016/j.neuropharm.2011.02.016 
Masha Burelo  is a PhD Student at the University of Aberdeen. Her research explores Electrophysiology and behavioural evaluation in preclinical models of Alzheimer’s disease. Masha started her studies in veterinary medicine in Mexico and first became interested in cannabinoids when her dog developed epilepsy, then with close family members struck by Alzheimer’s Disease her interest in neuroscience, plants and the brain developed.