Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism most of the penis is hard; however, the glans penis is not. In nonischemic priapism the entire penis is only somewhat hard. Sickle cell disease is the most common cause of ischemic priapism. Other causes include medications such as antipsychotics, SSRIs, and blood thinners, as well as drugs such as cocaine and cannabis. Ischemic priapism occurs when blood does not adequately drain from the penis. Nonischemic priapism is typically due to a connection forming between an artery and the corpus cavernosum or disruption of the parasympathetic nervous system resulting in increased arterial flow. Nonischemic priapism may occur following trauma to the penis or a spinal cord injury. Diagnosis may be supported by blood gas analysis of blood aspirated from the penis or ultrasound.