Cannabidiol (CBD) is the second major cannabinoid which is often said to improve anxiety and sleep with no psychoactive effect. It is said that CBD can promote the production of wake-related neurotransmitters such as dopamine. Further, co-injection of CBD and THC increased sleeping time in rats. However, no study has been done for the in-vivo effect of CBD to circadian clock. Present study aimed to elucidate whether CBD can modify peripheral circadian rhythm.
PER2::LUC knock-in female mice were used to determine the effect of CBD to the peripheral clock. Mice were divided into six groups: CBD isolate (99% crystalline) in MCT oil, CBD isolate in 5% EtOH/5% cremophor/water, and water-soluble CBD nanopowder in water, with respective vehicle controls. Each drug was orally administered at ZT4 or ZT16 for three days, then PER2 gene expression in the liver, kidney, and submandibular gland is observed by in-vivo imaging.
We found that phase advance in the liver and the submandibular gland only happens when MCT or CBD in MCT (CBD/MCT) was administered at ZT4. However, the phase advance did not differ between the MCT and CBD/MCT groups. Furthermore, neither the vehicle nor the CBD affected the peripheral clock when administered at ZT16. 
This study suggested that not CBD but rather MCT oil affect the circadian clock in mice. As MCT oil is commonly used as a base for CBD products, we propose that MCT might be the possible factor that affects the circadian clock and cause rhythm improvement. Therefore further detailed studies on the effect of CBD products will be needed.