Abstract The popularization of the use of electronic has become a global trend, and children are exposed to devices at younger ages. A large proportion of children and adolescents spend on screen time more than 2 h which is recommended in most guidelines. The paper reviews possible effects of screen time on physical and mental health, as well as mental disorders in children and adolescents. It is found that excessive screen time showed negative impacts on mental health, including depression, anxiety, mood disorder, social adaptational problems, behavioral disorders, self injurious behaviors, and health risk behaviors. Much attention has been paid on the association between excessive screen time and mental health of children and adolescents, while possible mechanisms and influencing factors are lacking. Effective intervention studies are needed to provide a basis for child and adolescent health promotion.

Cannabis is a traditional industrial crop that has been used for thousands of years for medicines， foods， and textiles. Due to its active components， cannabis has attracted extensive attention in the pharmaceutical industry at home and abroad. Currently， 55 countries around the world have legalized medical marijuana， and two provinces in China， Yunnan and Heilongjiang， can legally cultivate and process industrial hemp. However， the low content of cannabidiol （CBD） in industrial hemp is not conducive to subsequent development and research. Based on this， the author took medicinal cannabis， defined by CHEN Shilin′s team as tetrahydrocannabinol （THC） content<0.3% and high CBD content， as the research object， and reviewed four aspects of the active ingredients of medicinal cannabis， the isolation and purification technology of CBD， the development and application of cannabinoid-related products and the breeding methods of medicinal cannabis. Through combing， it is suggested that subsequent research should focus on excavation of genes of CBD synthesis， molecular breeding of evolutionary cannabis by gene editing technology， development of green extraction process， discovery of more active ingredients， and high yield of CBD through synthetic biology and cell-free system， with a view to provide reference for the development and application of medicinal cannabis in China.