Figure 1.

The concept of spectrum of atypia was recently introduced to classify atypical antipsychotics (AAPs). They can be divided in three categories, where risperidone is least atypical (Level I) and clozapine is most atypical (Level III), while all others fall within these two extremes of the spectrum (Level II). The molecular targets shown on the right add up, beginning with the D2 and 5-HT2A,C receptors that are common targets for all AAPs, extending to additional mechanisms such as M1 positive allosterism and GlyT (glycine transporter) activity that seem specific to clozapine. Other targets, such as H1 and α2 receptors and BDNF, are relevant to both Level II and III of atypia [7].