Orexin, ghrelin, neuropeptide-Y, melanin-concentrating hormone, GHRH, endorphins, cannabinoid, galanin, and nociceptin (OFQ) are orexigenic peptides, whereas melanocortin, GLP-1, corticotropic-releasing hormone, oxytocin, neuromedin U, and neurotensin act as anorexic peptides (for review, [114,115]). Appetite changes, bodyweight loss, and obesity have frequently been associated with psychiatric disorders. The gene discussed is GHRL; the disease is obesity due to melanocortin 4 receptor deficiency.