With the rapid and intensive spread of marihuana abuse among youth, Japanese society is focusing on law enforcement against drug abusers. In 2016, a mass killing allegedly committed by a marihuana abuser was reported in Japan.

To consider that common recognition of the diverse process and potential risks of cannabis psychosis should be shared among psychiatrists.

Elicit differences between cannabis psychosis and methamphetamine psychosis, and determine whether specific guidelines for treatment of cannabis psychosis are required.

Intensive retrospective review of distinctive methamphetamine and cannabis psychosis through case studies in our hospital.

Major symptoms of methamphetamine psychosis include auditory hallucination and paranoia, however recovery is achieved soon after undertaking treatment. In cannabis psychosis, distinctive features are megalomania and by a pseud-enlightenment experience of supernatural existence, abusers stick to an unrealistic self-estimate of omnipotent, which leads them to refuse the fading away of this feeling and repeat abuse.

Psychological substances have strong suggestibility so abusers’ symptoms are easily modified by their mental state. Involvement of syndicate or perception of illegality reflects abusers’ drastic symptoms, but after dehospitalisation, recurrences are relatively fewer. Cannabis, however, grows wild and is admitted legally in some countries, so abusers lack awareness of guilt by mistaken perception of omnipotence and unrealistic optimism. Due to addiction and depersonalization, they rather enjoy gaining contact with supernatural power and fall into social withdrawal and are implicated to social problems. Considering the difficulty of rehabilitating and returning abusers to the community, we should not disregard the risks of cannabis abuse.