The recommended dose of adjunctive brexpiprazole in MDD (2–3 mg/day) factors in CYP considerations; concomitant use of brexpiprazole with strong CYP2D6 inhibitors (e.g., paroxetine, fluoxetine) increases the exposure of brexpiprazole compared to the use of brexpiprazole alone [27]. The gene discussed is CYP2D6; the disease is major depressive disorder.