Cannabis is the most commonly used illicit substance amongst people with psychosis, and continued cannabis use following the onset of psychosis is associated with poorer functional and clinical outcomes. Yet, is it true that the role of cannabis use in causing psychotic episodes has been greatly underestimated because its use is so common and still widely believed by many to be, if anything, a benign calming influence?

Unfortunately, this is very much the case that its hazards are greatly underestimated. It is a causal factor in many situations where there is impairment of neurologic functioning of varied kinds, and this is very true of the association with severe mental illness as well as many minor complaints about emotions and aberrant behavior, and the impairment of physical performance in various respects such as the ability to drive a motor vehicle safely. There is a growing incidence of automobile accidents as well as out-of-control behavior and emotional extremes that are destructive either acutely or from changes that affect a person on a chronic basis. This has yet to be put into a definitive profile with hard data that will be convincing, first to the professionals, and then to the general public. Those who follow the literature see the signs clearly that there are dangers with extreme mental disturbance, which of course is the most serious end of the spectrum and can be life-threatening to the self or others.