Sildenafil is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity.


Sildenafil is the same medication found in the brand name Viagra. It is considered to be a generic version of the medication and therefore is a much cheaper option. Although it is the same chemical compound, it is only FDA approved for the treatment of pulmonary hypertension at the 20 mg dose. Using Sildenafil for erectile dysfunction is considered an off label use.

Sildenafil was initially designed to help lower blood pressure but is now typically used to treat erectile dysfunction.

Viagra is the brand name for Sildenafil Citrate and is used to treat erectile dysfunction.

Originally developed by scientists in the United Kingdom, it was brought onto the market by Pfizer Inc., an American pharmaceutical company.


Sildenafil can help men who cannot achieve or sustain an erection due to erectile dysfunction. It improves the erectile response when a man is already sexually stimulated, but it does not provide sexual stimulation. If there is no sexual stimulation, Viagra will not work.


According to clinical trial results, the most common side effects include:
  • Headaches
  • Nasal congestion
  • Impaired vision
  • Photophobia (sensitivity to light)
  • Dyspepsia (indigestion)
  • Less commonly, some users have experienced cyanopsia, where everything appears to have a tinted blue tinge.
  • In very rare cases, Sildenafil use can lead to nonarteritic anterior ischemic optic neuropathy, or damage to the optic nerve.
Other potential side effects include:
  • Rarely, priapism, a painful, long-lasting erection
  • Heart attack
  • Sudden hearing loss
  • Increased intraocular pressure
  • Ventricular arrhythmias
  • Since 2007, Sildenafil’s labeling in the United States has included a warning of the potential risk of sudden hearing loss.
  • Sildenafil can decrease blood supply to the optic nerve, causing sudden vision loss. This very rare adverse event occurs mainly in people with heart disease, hypertension, diabetes, high cholesterol, or pre-existing eye problems. Nobody really knows whether the vision loss was caused by the Sildenafil.


People with HIV who take protease inhibitors should discuss using Sildenafil with their doctors, because protease inhibitors increase the likelihood and severity of side effects. Experts say that these individuals should have no more than 25 milligrams (mg), and not more often than every 48 hours.

If the individual is taking alpha-blockers, they should make sure they take Viagra at least 4 hours before or after to prevent dangerously low blood pressure.


The following individuals should not take Sildenafil, or should check with their doctor first:
  • Those on nitric oxide donors, nitrates, and organic nitrites
  • Men who are advised to refrain from sexual intercourse because of cardiovascular risk factors
  • People with severe liver impairment
  • People with kidney disease
  • Individuals with low blood pressure (hypotension)
  • Those who have had a recent heart attack or stroke
  • Individuals with hereditary degenerative retinal disorders
A Sildenafil overdose can be serious, although death is rare. A Sildenafil overdose can be serious. If you believe you have had more than the standard dosage, call a doctor or local Poison Control Center.


  • Vomiting
  • Blurred vision and distorted vision
  • Papilledema – swelling in the optic nerve
  • Optic Neuropathy – damage to the optic nerve
  • Tachycardia (increased heart rate)
  • Prolonged priapism
  • Blindness
  • Rhabdomyolysis – break down of muscles
  • Diarrhea
  • Deaths from Sildenafil overdose are rare but possible.