Sexual dysfunction is common with selective serotonin reuptake inhibitor use for major depressive disorder. Studies have shown associations between genetic variation in the adenosine triphosphate (ATP)-binding cassette, subfamily B, member 1 gene (ABCB1), which encodes the drug efflux transporter P-glycoprotein (PGP), and selective serotonin reuptake inhibitor response. This study measured functionally implicated ABCB1 variants (rs2235015, rs1128503, rs2032582, and rs1045642) and sexual dysfunction using the Changes in Sexual Functioning Questionnaire. This study included outpatients (18-40 years of age) treated for major depressive disorder with a selective serotonin reuptake inhibitor for 6 weeks. Changes in Sexual Functioning Questionnaire outcomes were stratified by ABCB1 genotype and PGP substrate status. The authors recruited 82 individuals (22 men and 57 women). Women receiving a PGP substrate with a rs1128503 TT genotype had a significantly lower Changes in Sexual Functioning Questionnaire total score (37.2 ± 5.4), indicating greater sexual dysfunction, than did those with the CT (42.9 ± 6.3) or CC genotypes (46.6 ± 5.6), F(2) = 6.00, p = .005, p = .02, with multiple testing correction. The results indicate a relationship between genotypes at rs1128503, total sexual dysfunction, and PGP substrates use for women and may explain some of the sexual dysfunction variability seen with selective serotonin reuptake inhibitor treatment. Results need to be confirmed with a larger sample size that includes men.