Excessive Red Blood Cells
Polycythemia is a medical condition in which there is an overproduction of red blood cells. A 2010 study in the European Journal of Endocrinology shows that testosterone use causes polycythemia. This investigation also noted an association between testosterone and erythropoietin, the hormone triggering red blood cell production. These findings suggest that the polycythemia commonly found in testosterone replacement therapy results from excessive testosterone levels. Keeping these levels low with alternate delivery methods may prevent this unwanted side effect.