Despite all of the uncertainties surrounding the cannabis-psychosis link, we are left with the task of translating these results into clear recommendations for our patients. The evidence suggests that cannabis is associated with an increased risk of psychosis when it is used frequently. Whether cannabis can trigger a primary psychotic disorder that would not have otherwise occurred is unclear. However, in most individuals who use cannabis, psychosis does not develop, which suggests that the increased risk must be related to other vulnerability factors (genetics, frequency, or age of onset of cannabis misuse).
Cannabis also seems to alter the clinical course of schizophrenia negatively. While meta-analyses suggest better cognitive function among cannabis-using patients, this may be a reflection of a higher-functioning subgroup of schizophrenia patients. Accordingly, cannabis-using patients who achieve abstinence may demonstrate improved symptoms and cognitive performance.
The first step in communicating this information to our patients consists of screening for cannabis use and obtaining a thorough substance use history. Psychoeducation and early interventions for young patients who may be vulnerable to psychosis should be used, and motivational interviewing and cognitive-behavioral therapy should be considered to encourage reduction and cessation of use.
There are no accepted pharmacological treatments for cannabis use disorders, yet several potential agents are under investigation. Future studies that control for both environmental and biological risk factors are needed to more clearly elucidate the mechanisms linking cannabis misuse to psychosis.