Which medication is known as an erythropoiesis-stimulating agent?

Erythropoietin is an essential hormone produced primarily by the kidneys that plays a critical role in the regulation of red blood cell production, a process known as erythropoiesis. As an erythropoiesis-stimulating agent, its primary function is to stimulate the bone marrow to increase the production of red blood cells in response to low oxygen levels in the blood or anemia. This characteristic makes erythropoietin a vital treatment for patients with conditions like chronic kidney disease, where natural production may be insufficient.

The other medications listed do not share this specific role. Compazine is primarily used as an anti-psychotic and anti-nausea medication. Dronabinol is a synthetic form of THC, used to treat nausea and vomiting as well as to stimulate appetite in patients undergoing chemotherapy. Varubi is used for the prevention of nausea and vomiting associated with chemotherapy but does not affect red blood cell production. Hence, erythropoietin stands out as the only option that directly stimulates the production of red blood cells, making it the correct answer.