A 2021 review on the effects of cannabinoids on sleep stated the two exogenous cannabinoids, tetrahydrocannabinol (THC) and cannabidiol (CBD), have different actions on the CB1 and CB2 receptors. The authors noted that CB1 receptors had been shown to enhance the activation of the serotonergic system, causing a regulatory effect on the sleep-wake cycle. While THC mainly works on the CB1 receptors, it may have dose-dependent effects. Most of the studies examining cannabinoid effects on sleep were initially polysomnography-based, including several animal and small human studies. The authors concluded that while acute administration of THC has been associated with decreased rapid eye movement (REM) sleep, the effects of chronic use of THC on the REM stage are not consistent. [1]
A 2017 review included studies on cannabis and specific sleep disorders from 2014 to the time of publication. The authors described that while THC acts on CB1 and produces a dose-based biphasic effect, preclinical studies suggested that circadian rhythms are less affected during THC administration. A study by Nicholson et al. found 15 mg THC increased sleepiness and decreased sleep latency the following morning. Another study by Dzodzomenyo et al. indicated that patients who screened positive for THC had more excessive daytime sleepiness symptoms and were more likely to meet the criteria for narcolepsy. Gorelick and colleagues in a synthetic THC administration study noted that THC decreased the amount of nighttime sleep over time suggesting a potential effect of tolerance. Overall, the authors concluded that the research (dating back to the 1970s) on the impact of cannabis in sleep have shown mixed results with some work showing a decrease in onset latency and wake after sleep onset, others observed an increase in slow wave sleep and a decrease in REM. [2]
A 2019 animal study observed the effects of acute vaporized cannabis on sleep and electrocortical activity in rats. Animals were treated with 0 (control), 40, 80 and 200 mg of cannabis immediately before polysomnographic recordings. While cannabis 200 mg increased non-rapid eye movement (NREM) sleep time during the light phase, no changes in sleep were observed during the dark (active) phase. Total duration of rapid eye movement (REM) phase during the light phase was 33.6 ± 6.1 min in the cannabis 200 mg group vs. 32.6 ± 5 min in the control group. REM episodes duration were similar between the two groups (1.5 ± 0.3 vs. 1.5 ± 0.1). The Cannabis 200 mg group had a greater (non-significant) number of REM episodes (27.0 ± 8.8 vs. 22.5 ± 2.9). The authors suggested that as THC is a partial CB1 agonist, it would cause a greater effect during the lights-on period when the levels of CB1 receptors are high and administration of medicinal cannabis during the resting phase of the day may be optimal to treat sleep difficulties. [3]