Several classes of drugs are used to treat obesity, including GLP-1 receptor (GLP-1R) agonists, agonists of glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptors, lipase inhibitors, sympathomimetics, and dopamine and norepinephrine reuptake inhibitors with the addition of an opioid antagonist, in particular bupropion/naltrexone [145]. Here, GIP is linked to obesity due to melanocortin 4 receptor deficiency.