What does augment the risk to use cannabis on an everyday-basis in psychotic patients?

Introduction There are strong enough evidences of the fact that risk of psychosis is augmented by cannabis use. In a recent analysis, the strongest predictor of case-control status was daily-skunk use, i.e. the ORs for skunk users increase with the frequency of use5. We know also that FEP who smoked cannabis in their lifetime are less neuropsychologically impaired i.e. they have better premorbid and current IQ6. In this study we wanted to test what augments the probability to be everyday users, taking into account premorbid social and academic adjustment and cognition as predictors, along with age at first cannabis-use and % of THC in cannabis used. Methods The sample was made of 834 First Episode Psychosis (FEP) cannabis-using and non-using patients from different European countries and 1.061 healthy controls, as part of the EUGEI-STUDY. A logistic regression was computed, using frequency of cannabis use among those who reported to have used cannabis in their lifetime, as an outcome variable in order to estimate the risk to be an everyday-user (heavy user) or a less-than-everyday user (recreational user), taking into account a list of predictors: sociodemographics, age at first cannabis-use, % of THC, premorbid social factor (PSF), premorbid academic factor (PAF), extracted from the Premorbid Adjustment Scale (PAS) and the four scales of WAIS-brief version. Results The risk to be an everyday-smoker was higher for cases, in interaction with age at first use, i.e. while the risk of controls diminishes when age at first use increases, this is not true for cases, whose risk stay higher even when age at first use increases (OR=1.2, p=0.001, CI 95% 1.09, 1.45). THC absolute concentration >10% augmented almost 2 folds the risk to be an everyday-smoker (OR=1.8, p=0.001, CI 95% 1.29, 2.60). A lower premorbid academic adjustment (OR=0.8, p=0.040, CI 95% 0.68, 0.99) and higher premorbid social adjustment before 16 years (OR=1.6, p=0.019, CI 95% 1.08, 2.60) increased the risk to be a heavy cannabis user, along with having a lower education level and being unemployed (all p<0.05). Higher scores of working memory reduced the risk related to education and premorbid adjustment. Conclusions The predictors of everyday cannabis-­use were lower premorbid academic adjustment but higher sociability before 16 years, the latter moderated by a higher working memory. An earlier age at first use was the most relevant risk factor for being cannabis everyday-­users in both psychotic subjects and healthy controls.