According to Kapur et al. (1998) [54], a dose of olanzapine above 30 mg/day induced hyperprolactinaemia equivalent to the one induced by risperidone due to binding with D2 receptor occupancy, while other reports suggest that dopamine D2 receptor occupancy of risperidone is lower than olanzapine. This evidence concerns the gene DRD2 and hyperprolactinemia.