ABCB1 encodes P-glycoprotein, an ATP-dependent efflux pump that translocates diverse substrates including drugs and phospholipids across cellular membranes 123. The protein catalyzes ATP-driven translocation of phosphatidylcholine, phosphatidylethanolamine, and sphingomyelins from the cytoplasmic to exoplasmic leaflet 3. Structurally, ABCB1 possesses a substrate-binding site within one transmembrane domain, with transmembrane helix 4 playing a central role in conformational transitions necessary for substrate recognition and transport 4. ABCB1's broad substrate specificity enables multidrug resistance in cancer cells through energy-dependent drug efflux, limiting intracellular accumulation 12. At the blood-brain barrier, P-glycoprotein protects the central nervous system by actively extruding substrates including certain antidepressants 5. Clinically, ABCB1 polymorphisms show variable associations with drug responses. Specific SNPs (rs2032583, rs2235015) significantly predict antidepressant treatment outcome in hospitalized patients with major depression 5. However, common polymorphisms (C3435T, C1236T, G2677T/A) do not reliably predict chemotherapy response in breast cancer 6. The TTT haplotype (1236TT-2677TT-3435TT) associates with violent suicide attempt methods, particularly in first-time female attempters 7. Limited evidence suggests associations between specific ABCB1 variants and glucocorticoid-induced avascular necrosis and colorectal cancer risk in Asian populations 89.