What is the name of the hormone that stimulates red blood cell production?

The hormone that stimulates red blood cell production is erythropoietin, often abbreviated EPO.

Erythropoietin is a glycoprotein hormone produced mainly by specialized cells in the kidneys. When the kidneys detect reduced oxygen availability, they release more EPO into the bloodstream. The hormone travels to the bone marrow, where it binds to receptors on developing red-cell precursors and promotes their survival, multiplication, and maturation. More red blood cells can then improve the blood’s oxygen-carrying capacity.

EPO is part of a feedback loop rather than an always-on production switch. Healthy adults produce small amounts continuously to replace aging red cells, while anemia, blood loss, or low blood oxygen can increase production substantially. The liver contributes more to EPO production before birth and remains a secondary source after birth.

The concept of a blood-borne factor regulating red-cell formation was proposed by Paul Carnot in 1905. EPO was purified in 1977, its human gene was isolated in 1985, and synthetic EPO was used clinically by 1987. Testosterone can influence red-cell production indirectly, but erythropoietin is the specific hormone that directly drives erythropoiesis.