Although, in human T2DM islet cells, the expression of 5-HT2CR has not been observed [31], the 5-HT2CR agonist Belviq (lorcaserin) is the first FDA-approved drug to treat obesity in 15 years [52], and central serotonin 2C receptors regulated glucose homeostasis and may represent a rational target for type 2 diabetes (T2DM) treatment [53, 54]. This evidence concerns the gene HTR2C and type 2 diabetes mellitus.