Viagra is one of the most controversial and widely discussed pharmaceutical drugs to have hit the market in the last 30 years. People most commonly use Viagra to treat erectile dysfunction.

It works by relaxing the muscles in the walls of blood vessels in certain areas of the body. In most cases, Viagra works well and has changed people's lives for the better.

The word Viagra is the brand name for sildenafil citrate and is used to treat erectile dysfunction and pulmonary arterial hypertension.

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

Viagra is also sold under brand name Revatio. Sildenafil citrate's chemical formula is C22H30N6O4S.

In this article, we look briefly at the effects of Viagra, why it is used, the side effects, and history.

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

Viagra is generally safe to use in moderation. However, taking it may cause a range of adverse effects.

According to clinical trial results, the most common side effects include:

Less commonly, some users have experienced cyanopsia, where everything appears to have a tinted blue tinge.

In very rare cases, Viagra use can lead to nonarteritic anterior ischemic optic neuropathy, or damage to the optic nerve.

Other potential side effects include:

Since 2007, Viagra's labeling in the U.S. has included a warning of the potential risk of sudden hearing loss.

Viagra 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. The link between vision loss and Viagra is as yet unknown.

Interactions

People with HIV who take protease inhibitors should discuss using Viagra with their doctors. Protease inhibitors increase the risk and severity of side effects. These individuals should have no more than 25 milligrams (mg) of Viagra at a time, and not more often than every 48 hours.

Individuals taking alpha-blockers should make sure they take Viagra at least 4 hours before or after taking alpha-blockers. This can help prevent dangerously low blood pressure.

Contraindications

The following individuals should not take Viagra, or should check with their doctor first:

  • people 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

Some athletes take Revatio to increase their exercise capacity, but there is little evidence to support this use.

Effects

Viagra 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.

When sexual stimulation occurs, nitric oxide is released by the nervous system in the erectile tissue of the penis. Nitric oxide stimulates an enzyme that produces messenger cyclic guanosine monophosphate (cGMP).

cGMP causes the arteries in the penis to dilate, so that the arteries and the erectile tissue fill with blood. An erection results.

Viagra prevents cGMP from becoming degraded, so the blood flow and the erection can continue.

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A viagra overdose can be serious, although death is rare.

The dosage will be different if the drug is taken for erectile dysfunction or for pulmonary arterial hypertension.

Viagra

For erectile dysfunction, Viagra comes in blue, diamond-shaped pills, in doses of 25, 50, or 100 mg.

The individual takes a maximum of one pill in a 24-hour period, 30 minutes to 1 hour before sexual intercourse.

Revatio

For pulmonary arterial hypertension, Viagra comes in white, round, film-coated tablets. People take one 20-mg Revatio tablet three times a day.

Viagra overdose

A Viagra overdose can be serious. If you believe you have had more than the standard dosage, call a doctor or local Poison Control Center.

symptoms of an overdose might include:

  • 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 viagra overdose are rare but possible.

Initially, Viagra was designed by Pfizer scientists working in the U.K. They were, in fact, working on a drug for hypertension, or high blood pressure, and angina pectoris, a symptom of ischemic heart disease.

During the phase 1 trials, it was noted that the drug did very little to prevent angina but did induce marked penile erections. Hitting the market in 1998, Viagra was the first oral treatment approved to treat erectile dysfunction in the U.S.

Viagra's meteoric rise to fame has seen it enter usage as an illicit drug. But, Viagra use in individuals without erectile dysfunction does not seem to have any effect. Although, researchers have noted that there is a significant placebo effect. On a similar note, there is no proven benefit for women taking the drug.

In 2008, Viagra generated some $1.93 billion of revenue for Pfizer.