This protein is present at the blood–brain barrier where it functions as a drug transporter.[17–19] ABCB1 acts as an efflux transporter for many substrates such as chemotherapeutic agents, anti-epilepsy medicine, or drug and antibiotics for PD.[20–22] Thus, the function disorder of ABCB1 gene may be a risk factor for Parkinson's disease. This evidence concerns the gene ABCB1 and Parkinson disease.