Cancer Connect.com says that some drugs, such as Marinol, stimulate appetite by blocking the cannabinoid-1 receptor in the brain that is responsible for chemotherapy-induced nausea and vomiting. According to Care Search, the exact mechanism through which many appetite stimulants act is unknown.
The National Cancer Institute says that progesterone hormones such as megestrol acetate have been clinically observed to improve appetite and promote weight gain, particularly of body fat. Glucocorticosteroids may improve appetite through their euphoric and anti-inflammatory actions.
Cancer Connect.com explains that anorexia, or loss of appetite, is a common problem in cancer patients. Many cancer patients lose a significant amount of weight due to anorexia.