An increasing number of studies have followed this rationale, sub-stratifying patients and linking pharmacogenetic (PGx) variability of CYP2D6 and CYP2C19 to drug blood-concentrations, the treatment response, and the remission rates in patients with depression [20], aiding in the creation of the Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for CYP2D6 and CYP2C19 Genotypes [21]. The gene discussed is CYP2D6; the disease is major depressive disorder.