Certain drugs may increase appetite either as their primary effect or as a side effect. Antidepressants, such as mirtazapine or amitriptyline , and antipsychotics, particularly chlorpromazine and haloperidol , as well as tetrahydrocannabinol (found in cannabis ), all present an increase in appetite as a side effect. In states where it is approved, medicinal cannabis may be prescribed for severe appetite loss, such as that caused by cancer , AIDS , or severe levels of persistent anxiety . Other drugs or supplements which may increase appetite include antihistamines (such as diphenhydramine , promethazine or cyproheptadine  ), and B vitamin supplements (such as vitamin B12 and vitamin B-complex ).
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 .