GHRL and obesity due to melanocortin 4 receptor deficiency: Since recent studies have demonstrated the possibility to specifically target cells responding to a particular hormone by chemically hybridizing drugs to various gut hormones [292,301], a similar potential avenue for anti-obesity drugs might be to hybridize ghrelin to cytotoxic or neurotoxic drugs aiming to either permanently or reversibly block neuronal activity of ghrelin-targeted cells.