CNR1 and obesity due to melanocortin 4 receptor deficiency: We chose to review the screen results for body fat from these KO lines to determine if any or all shared the lean phenotype of Cnr1 KO mice, and if so to examine them in greater detail to determine how closely other phenotypic characteristics mirrored those of Cnr1 KO mice, including behavioral phenotypes that suggest the possibility of on-target neuropsychiatric side-effects which would likely preclude developing inhibitors of these enzymes as anti-obesity drugs for humans.