A long-term study of sleep quality assessed CBD actions using a common self-report instrument found a modest improvement in sleep, and more patients with improved sleep compared to poorer sleep (Shannon et al., 2019). Most studies on the effects of cannabinoids in sleep, and in general, have focused on the effects of purified THC, or cannabis preparations with relatively high levels of THC compared to other phytocannabinoids. However, recent interest in therapeutic roles for CBD has ushered in further studies focusing on CBD, including its effects on sleep. In one study, mixed effects of combined THC and CBD have were reported, with THC generally increasing sedation and CBD having opposing, wake-enhancing effects (Nicholson et al., 2004). A long-term study of sleep quality assessed CBD actions using a common self-report instrument found a modest improvement in sleep, and more patients with improved sleep compared to poorer sleep (Shannon et al., 2019). Notably, a study using the Sativex extract formulation (containing approximately equal ~2 mg doses of THC and CBD) to examine sleep in subjects with pain-related sleep disturbances (Russo et al., 2007) reported improved sleep with no evidence of tolerance to the drug action. Thus, there may be cannabis formulations that support sustained sleep improvement. A recent controlled clinical study assessing the acute pharmacodynamic effects of 100 mg of CBD or CBD-dominant cannabis found that vapor inhalation of the latter increased subjective sleepiness. The investigators noted that CBD alone did not have significant effects on sleepiness, so possibly the effects of the CBD-dominant cannabis were due to the relatively small amounts of THC in their CBD-dominant cannabis preparation (Spindle et al., 2020). Indeed the amount of THC in their case was 3.7 mg, a similar concentration as found in many “full spectrum,” <0.3% THC, commercial CBD products (Corroon and Kight, 2018), indicating further controlled research into the physiological effects of these commercial products is necessary. It is still unclear whether acute administration of this relatively low dose of THC alone is enough to produce sleepiness, or whether it has synergistic effects with CBD and other phytocannabinoids in the strain of CBD-dominant cannabis used in this study.