Sildenafil Citrate would not be effective in men that have erectile dysfunction caused by severe arterial deformities, loss of tubular smooth muscle cells, or incompressible cavernosal veins.

Sildenafil Citrate has very minor to moderate side effects, which usually last a few minutes to a few hours after dosage. This drug can also cause dilation of blood vessels in other parts of the body, causing headaches and fainting.

Other side effects include:

• Blurred vision
• Dyspepsia
• Facial flushing
• Rhinitis
• Sensitivity to light
• Upset stomach

These side effects occur more often as the dosage increases.

The most serious side effect would be blue tinted vision. Sildenafil Citrate can also block the breakdown of cyclic GMP in the cone cells of the retina in some way that leads to this perception of blue. Contact lenses with tiny electrodes which record the retina's electrical activity can be used to determine how Viagra affects this blue vision in the long term.

Laboratory tests have concluded that there is no evidence of abnormalities or an increased heart rate caused by Sildenafil Citrate.