<p>The mechanism of action of brexpiprazole in the treatment of major depressive disorder or schizophrenia is unknown. However, the efficacy of brexpiprazole may be mediated through a combination of partial agonist activity at serotonin 5-HT1A&nbsp;and dopamine D2&nbsp;receptors, and antagonist activity at serotonin 5-HT2A&nbsp;receptors.</p>