It is not really known what causes priapism. Men who suffer from priapism sometimes have blood diseases like leukemia (a type of cancer of the blood; in the United Kingdom and some other countries it is spelled "leukaemia") or sickle-cell disease (which makes the blood cells crescent-shaped). Problems with the nervous system such as injury to the spinal cord or abnormal growths on it can also lead to priapism. Certain medicines can make priapism happen, including some used to treat ED such as alprostadil. A 2008 study suggests that too much of the chemical adenosine in the body may cause priapism since it makes blood vessels widen which lets more blood flow into the penis.