Only a small proportion of the cases of erectile dysfunction are caused by a hormone deficiency. In those cases, the most common cause is a testosterone deficiency. This can be replaced in hormone replacement therapy.
The most commonly used form of this therapy is the depot formulation of the long-acting esters of testosterone. The esters are converted to free testosterone in the circulation. Oral preparations have the problem of unpredictable blood levels of testosterone, and the risk of liver damage.