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
Side effects
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, Viagra 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, Viagra's labeling in the United States 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. Nobody really knows whether the vision loss was caused by the Viagra.
Viagra interactions
People with HIV who take protease inhibitors should discuss using Viagra 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.
Viagra contraindications
The following individuals should not take Viagra, 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
Some athletes take Revatio to increase their exercise capacity, but there is little evidence to support this use.
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