There are several known associations between polymorphisms in the P-gp (ABCB1) gene and increasing occurrence of adverse effects to various pharmaceutical compounds, for example, olanzapine,17, 24 selective serotonin reuptake inhibitors12, 14 and nortriptyline.13 Furthermore, a Japanese population study supports that such polymorphisms may be directly linked to the metabolic disturbances and obesity.19 Reduced mRNA expression of the ABCB1 gene might be a direct consequence of circulating pro-inflammatory cytokines in obese individuals. Here, ABCB1 is linked to obesity due to melanocortin 4 receptor deficiency.