CYP2C19 and major depressive disorder: This is in line with a recent study by Fan and Bousman which estimated that up to one-third of US and Canadian patients treated for major depressive disorders carry actionable CYP2C19 and CYP2D6 genetic variants and could benefit clinically from pairing CYP2C19 and CYP2D6 testing with the STAR*D treatment algorithm conferring greater effect of CYP2C19 genotyping for the first two steps and CYP2D6 genotyping for the remaining 3 steps [10].