Cannabis abuse, mainly occurring among young people, is increasing in Japan as it is in many other countries. Some foreign countries have lifted the ban on recreational cannabis use and approving the use of cannabinoids, one of the compounds of cannabis, to treat incurable diseases. However, the possibility of mental disorders being caused by the smoking of cannabis has not yet been fully investigated. Most psychiatrists in Japan have no experience in treating cannabis related mental disorders, perhaps due to low number of people who abuse cannabis in the country. Unlike methamphetamine, which mainly consists of paranoia, cannabis psychosis often triggers religious and supernatural-related delusions. Although less psychedelic in nature, cannabis exhibits similar effects to those of psychedelic drugs, such as LSD, hallucinogenic cacti and mushrooms. This paper describes in detail the psychedelic experience characterized by altered states of consciousness by smoking cannabis and details how the traces of such experiences may persist even after the onset of toxic psychosis. Given that psychotic symptoms remain longer than methamphetamine psychosis, this paper also discusses the importance of a hospitalization period sufficient to prevent exacerbation in the long term, and to encourage abstaining from drugs through drug harm education.
 Author's abstract