P-glycoprotein (P-gp), a member of the ATP-binding cassette (ABC) transporter family, plays a vital role in drug distribution, barrier function, and disease mechanisms. It is highly expressed at biological interfaces such as the blood-brain barrier (BBB), gastrointestinal tract, liver and kidneys, where it actively effluxes xenobiotics and therapeutic agents, thereby affecting drug efficacy and resistance. Beyond drug delivery, P-gp is involved in neurodegenerative diseases, epilepsy and cancer resistance, making it a key target in clinical research.