The efflux pump, p-glycoprotein, controls bioavailability and excretion of pharmaceutical compounds. In the blood-brain barrier, p-glycoprotein regulates the delivery of pharmaceutical substances to the brain, influencing efficacy and side effects for some drugs notably antipsychotics. Common side effects to antipsychotics include obesity and metabolic disease. Polymorphisms in the ABCB1 gene coding for p-glycoprotein are associated with more severe side effects to neuro-pharmaceuticals as well as weight gain, indicating a potential link between p-glycoprotein function and metabolic regulation. Using microarray data analysis from 145 neurologically sound adults, this study investigated the association between body mass index (BMI) and ABCB1 expression in the frontal cortex. Increasing BMI values were associated with a statistically significantly reduced expression of ABCB1. Investigation of DNA methylation patterns in a subgroup of 52 individuals found that the methylation/expression ratios of ABCB1 were unaffected by increasing BMI values. Interestingly, the effect of BMI on ABCB1 expression appeared stronger in African Americans than in Caucasians.The Pharmacogenomics Journal advance online publication, 29 November 2016; doi:10.1038/tpj.2016.74.