Causes

An erection normally occurs in response to physical or psychological stimulation. This stimulation causes certain smooth muscles to relax, increasing blood flow to spongy tissues in the penis. As a result, the blood-filled penis becomes erect. After stimulation ends, the blood flows out and the penis returns to its nonrigid (flaccid) state.

Priapism occurs when some part of this system — the blood, vessels, smooth muscles or nerves — changes normal blood flow, and an erection persists. The underlying cause of priapism often can't be determined, but several conditions may play a role.

Blood disorders

Blood-related diseases might contribute to priapism — usually ischemic priapism, when blood isn't able to flow out of the penis. These disorders include:

• Sickle cell disease
• Leukemia
• Other blood diseases (hematologic dyscrasias), such as thalassemia and multiple myeloma

The most common associated diagnosis in children is sickle cell disease.

Prescription medications

Priapism, usually ischemic priapism, is a possible side effect of a number of drugs, including:

• Medications injected directly into the penis to treat erectile dysfunction, such as alprostadil (Caverject, Edex, others), papaverine, phentolamine (Oraverse) and others
• Antidepressants, such as fluoxetine (Prozac), bupropion (Wellbutrin XL, Wellbutrin SR), trazodone and sertraline (Zoloft)
• Alpha blockers including prazosin (Minipress), terazosin, doxazosin (Cardura) and tamsulosin (Flomax)
• Medications used to treat anxiety or psychotic disorders, such as hydroxyzine (Vistaril), risperidone (Risperdal), olanzapine (Zyprexa), lithium (Lithobid), clozapine (Clozaril), chlorpromazine and thioridazine
• Blood thinners, such as warfarin (Jantoven) and heparin
• Hormones such as testosterone or gonadotropin-releasing hormone
• Medications used to treat attention-deficit/hyperactivity disorder (ADHD), such as methylphenidate (Concerta, Ritalin, others) and atomoxetine (Strattera)

Alcohol and drug use

Alcohol, marijuana, cocaine and other drugs can cause priapism, particularly ischemic priapism.

Injury

A common cause of nonischemic priapism is trauma or injury to your penis, pelvis, or the region between the base of the penis and the anus (perineum).

Other factors

Other causes of priapism include:

• A spider bite, scorpion sting or other toxic infections
• Metabolic disorders including gout or amyloidosis
• Neurogenic disorders, such as a spinal cord injury or syphilis
• Cancers involving the penis