HTR2A and bipolar disorder: According to the original model proposed by Fountoulakis et al. [76], the stronger predictors for antidepressant efficacy in bipolar depression would encompass norepinephrine alpha-1, dopamine (DA) D1, and histamine antagonism, followed by 5-HT2A, by muscarinic and dopaminergic D2 and D3 antagonism, and eventually by norepinephrine reuptake inhibition and 5-HT1A agonist effect [76].