The short form of this polymorphism (ss) is associated with decreased clinical response to citalopram in children or adolescents with depression or anxiety.[7, 8] The variant allele 5HTTLPR-S coexisting with the CYP2C9*3 variant allele is found to be associated with an even greater risk of major depressive disorder.[9]. This evidence concerns the gene CYP2C9 and major depressive disorder.