The Netherlands Drug Situation 2010 - Trimbos-instituut

When having used cannabis during the past month, the chance to have psychologicalproblems was twice as high. Among males, it was found that almost 20% of the currentcannabis users reported psychological complaints, compared to only 10% among the nonusers. Among females, 28% of the current cannabis users reported psychological complaints,compared to only 14% among the non users. These associations remained significantafter correcting for demographic variables. There was no control for the use of othersubstances.In the past decade, various studies, both Dutch and international, have reported associationsbetween cannabis use and psychotic outcomes, ranging from subclinical symptomsto a full blown diagnosis of schizophrenia. In 2010 several Dutch studies on cannabis andpsychosis and one on cannabis use and depression spells were published.Schubart et al. (2010) showed that in a large (convenience) sample of nearly 18 thousandadolescents (mean age 21.6 years), only early onset of cannabis use (age 12 oryounger) was strongly associated with a top 10 score on subclinical positive psychoticexperiences and to a lesser degree with negative symptoms. Moreover, the investigatorsfound a dose-response relationship as expressed by the amount of money weekly spenton buying cannabis.Bossong & Niessink (2010) have postulated a causal mechanism explaining the linkbetween cannabis use during adolescence and psychosis. They argue that exogenouscannabis (THC) administration interferes with normal brain development during adolescence,by disrupting the process of strengthening and pruning of synaptic connections inthe prefrontal cortex regulated by the glutaminergic system.Machielsen et al. (2010) revealed that 45% of a sample of 169 patients psychotic disorderhad a comorbid cannabis use disorder, and this group experienced higher levels ofpositive symptoms, compared to psychotic patients without cannabis use disorder (excludingthose with another drug uses disorder).Finally, a patient-sibling and sibling-control study in the Netherlands and Flandersfound that a genetic risk for psychosis is associated with an increased sensitivity to thepsychotomimetic effects of cannabis (Genetic Risk and Outcome in Psychosis (GROUP)investigators, 2010). This differential sensitivity to cannabis was demonstrated in theform of greater response to recent (rather than lifetime) cannabis use in individuals athigher-than-average risk for psychotic disorder and related disordersAs described in § 10.3, the balance between THC and the cannabinoid CBD may becrucial in determining the psychotomimetic and possibly addictive effects of cannabis(e.g. Henquet, 2010). Dutch marihuana contains very low levels of CBD compared toTHC. Consequently, it is possible that certain health effects are more likely with this typeof cannabis compared to certain (imported) varieties of hashish, that have a lowerTHC/CBD ratio.In one cross-sectional study, based on the World Mental Health Surveys covering 50thousand respondents in 17 countries (including the Netherlands), associations werefound between early onset cannabis use (< 17 years) and later onset of depression spells(RR 1.5; De Graaf et al., 2010). This association remained unchanged after controllingfor a variety of confounder, but dropped to non-significance after controlling for childhoodconduct problems. Probably, propensity for norm violating behavior in youth maypredispose both to later cannabis use and depression.95