The results show that , in particular , frequent cannabis use , especially daily use , and the consumption of high-potency cannabis are associated with a higher risk of developing psychosis .
Moreover , several genotypes moderate the impact of cannabis use on psychosis risk , particularly those involved in the dopamine function , such as AKT1 .
Finally , cannabis use is associated with an earlier psychosis onset and increased risk of transition in individuals at a clinical high risk of psychosis .
These findings indicate that changing cannabis use behavior could be a harm reduction strategy employed to lower the risk of developing psychosis .
Increasing evidence indicates a relationship between  cannabis use and psychosis risk .
Specific factors , such as determinants of cannabis use or the genetic profile of cannabis users , appear to moderate this association .
The present systematic review presents a detailed and up-to- date literature overview on factors that influence the relationship between cannabis use and psychosis risk .
What causes psychosis? An umbrella review of risk and protective factors.
Psychosis is a heterogeneous psychiatric condition for which a multitude of risk and protective factors have been suggested . This umbrella review aim ed to classify the strength of evidence for the associations between each factor and psychotic disorders whilst controlling for several biases . The Web of Knowledge data base was search ed to identify systematic review s and meta-analyses of observational studies which examined associations between socio-demographic , parental , perinatal , later factors or antecedents and psychotic disorders , and which included a comparison group of healthy controls , published from 1965 to January 31 , 2017 . The literature search and data extraction followed PRISMA and MOOSE guidelines . The association between each factor and ICD or DSM diagnoses of non-organic psychotic disorders was grade d into convincing , highly suggestive , suggestive , weak , or non-significant according to a st and ardized classification based on : number of psychotic cases , r and om-effects p value , largest study 95 % confidence interval , heterogeneity between studies , 95 % prediction interval , small study effect , and excess significance bias . In order to assess evidence for temporality of association , we also conducted sensitivity analyses restricted to data from prospect i ve studies . Fifty-five meta-analyses or systematic review s were included in the umbrella review , corresponding to 683 individual studies and 170 putative risk or protective factors for psychotic disorders . Only the ultra-high-risk state for psychosis ( odds ratio , OR=9.32 , 95 % CI : 4.91 - 17.72 ) and Black-Caribbean ethnicity in Engl and ( OR=4.87 , 95 % CI : 3.96 - 6.00 ) showed convincing evidence of association . Six factors were highly suggestive ( ethnic minority in low  ethnic density area , second generation  immigrants , trait anhedonia , premorbid IQ , minor physical anomalies , and olfactory identification ability ) , and nine were suggestive ( urbanicity , ethnic minority in high ethnic density area , first generation immigrants , North-African immigrants in Europe , winter/spring season of birth in Northern hemisphere , childhood social withdrawal , childhood trauma , Toxoplasma gondii IgG , and non-right h and edness ) . When only prospect i ve studies were considered , the evidence was convincing for ultra-high-risk state and suggestive for urbanicity only . In summary , this umbrella review found several factors to be associated with  psychotic disorders  with different levels of evidence . These risk or protective factors represent a starting point for further etiopathological research and for the improvement of the prediction of psychosis
The results show that , in particular , frequent cannabis use , especially daily use , and the consumption of high-potency cannabis are associated with a higher risk of developing psychosis .
Moreover , several genotypes moderate the impact of cannabis use on psychosis risk , particularly those involved in the dopamine function , such as AKT1 .
Finally , cannabis use is associated with an earlier psychosis onset and increased risk of transition in individuals at a clinical high risk of psychosis .
These findings indicate that changing cannabis use behavior could be a harm reduction strategy employed to lower the risk of developing psychosis .
Increasing evidence indicates a relationship between  cannabis use and psychosis risk .
Specific factors , such as determinants of cannabis use or the genetic profile of cannabis users , appear to moderate this association .
The present systematic review presents a detailed and up-to- date literature overview on factors that influence the relationship between cannabis use and psychosis risk .