An orexigenic, or appetite stimulant, is a drug, hormone, or compound that increases appetite. This can be a naturally occurring neuropeptide hormone such as ghrelin, orexin or neuropeptide Y, or a medication which increases hunger and therefore enhances food consumption. Usually appetite enhancement is considered an undesirable side effect of certain drugs as it leads to unwanted weight gain, but sometimes it can be beneficial and a drug may be prescribed solely for this purpose, especially when the patient is suffering from severe appetite loss or muscle wasting due to cystic fibrosis, anorexia, old age, cancer or AIDS. There are several widely used drugs which can cause a boost in appetite, including tricyclic antidepressants (TCAs), tetracyclic antidepressants, natural or synthetic cannabinoids, first-generation antihistamines, most antipsychotics and many steroid hormones.
Agents with orexigenic effects include the following:
5-HT2C receptor antagonists/inverse agonists — mirtazapine, olanzapine, quetiapine, amitriptyline, cyproheptadine, lurasidone
H1 receptor antagonists/inverse agonists — mirtazapine, olanzapine, quetiapine, amitriptyline, cyproheptadine
Dopamine antagonists — haloperidol, chlorpromazine, olanzapine, risperidone, quetiapine
Adrenergic antagonists:
β blockers — propranolol, etc.
α2 adrenergic antagonists — mirtazapine, mianserin
Mixed α1/β blockers — carvedilol
α2 Adrenergic agonists — clonidine
CB1 receptor agonists (cannabinoids — THC/dronabinol (a component of Cannabis), nabilone
Corticosteroids — dexamethasone, prednisone, hydrocortisone
Certain pregnene steroids — megestrol acetate, medroxyprogesterone acetate
Anabolic steroids — oxandrolone, nandrolone, testosterone
Sulfonylurea antidiabetic drugs such as glibenclamide, chlorpropamide and tolbutamide
Mood stabilizers such as lithium
Some anti-epileptic drugs such as valproate, carbamazepine and gabapentin
α2δ VDCC ligands — gabapentin, pregabalin
Ghrelin receptor agonists such as anamorelin, GHRP-6, ibutamoren, ipamorelin, and pralmorelin
MC4 receptor antagonists
Insulin
Sugars such as fructose
