An erection normally occurs in response to physical or psychological stimulation. This stimulation causes certain blood vessels to relax and expand, increasing blood flow to spongy tissues in the penis. Consequently, 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, blood vessels or nerves — changes normal blood flow. Subsequently, an unwanted erection persists. Factors that can contribute to priapism include the following.

Blood disorders

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

  • Sickle cell anemia
  • Leukemia

Sickle cell anemia is the most common cause of priapism in boys. Sickle cell anemia is an inherited disorder characterized by abnormally shaped red blood cells. These abnormally shaped cells can block the flow of blood.

Prescription medications

Priapism, usually ischemic priapism, is a known side effect of a number of drugs. The following drugs can sometimes cause priapism:

  • Oral medications used to manage erectile dysfunction, such as sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra)
  • Drugs injected directly into the penis to treat erectile dysfunction, such as papaverine
  • Antidepressants, such as fluoxetine (Prozac) and bupropion (Wellbutrin)
  • Drugs used to treat psychotic disorders, such as risperidone (Risperdal) and olanzapine (Zyprexa)
  • Blood thinners, such as warfarin (Coumadin) and heparin

Alcohol and drug use

Misuse of prescription drugs, and alcohol and drug abuse can cause priapism, particularly ischemic priapism. Possible causes include:

  • Recreational use of erectile dysfunction drugs
  • Drinking too much alcohol
  • Use of illegal drugs such as marijuana or cocaine


A common cause of nonischemic priapism — a persistent erection caused by excessive blood flow into the penis — is trauma or injury to your genitals, pelvis or the perineum, the region between the base of the penis and the anus.

Other factors

Other causes of priapism include:

  • Spinal cord injury
  • Blood clots
  • Poisonous venom, such as venom from scorpions or black widow spiders

In some cases, doctors are unable to identify the specific cause for priapism.

June 15, 2013