Differences in craving for cannabis between schizophrenia patients using risperidone, olanzapine or clozapine

Substance abuse and psychotic disorders have a high rate of comorbidity. Both disorders are associated with changes in the dopaminergic transmission in the mesocorticolimbic pathways of the brain. Since antipsychotic medications interact with the dopamine receptors in these pathways, these medications could affect craving for substances. In the current study, the effect of clozapine (n = 27, mean dosage 350 mg), risperidone (n = 54, mean dosage 3.46 mg) and olanzapine (n = 60, mean dosage 13.78 mg) on subjective craving for cannabis was compared in 123 patients with cannabis dependence and psychotic disorder. Patients treated with risperidone reported significantly more craving compared with patients treated with clozapine (Z = -3.19, p =.001) or olanzapine (Z = -2.24, p =.025). No significant differences in craving between clozapine and olanzapine were found. These results are in concordance with findings in the literature on this subject and could be explained by differences in three dopamine mediated mechanisms of these compounds: 1) occupancy rate of dopamine D ₂ receptors, 2) dissociation rate of dopamine D ₂ receptors, 3) D ₁/D ₂ occupancy ratio. Risperidone and clozapine show a maximal difference in D2 receptor occupancy rate, dissociation rate and D ₁/D ₂ ratio. Olanzapine is intermediate between risperidone and clozapine in these characteristics.