Amongst sildenafil's rare but serious adverse effects are: priapism, severe hypotension, myocardial infarction, ventricular arrhythmias, stroke and increased intraocular pressure.
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Common side effects include sneezing, headache, flushing, dyspepsia, palpitations and photophobia.
Care should be exercised by patients who are also taking Protease inhibitors for the treatment of HIV. Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side-effects. It is recommended that patients using protease inhibitors limit their use of sildenafil to no more than one 25-mg dose every 48 hours.[citation needed
Some sildenafil users have complained of seeing everything tinted blue (cyanopsia). Some complained of blurriness and loss of peripheral vision. In May of 2005, the U.S. Food and Drug Administration found that sildenafil could lead to vision impairment and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy.
In October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including sildenafil, requires a more prominent warning of the potential risk of sudden hearing loss as the result of postmarketing reports of deafness associated with use of PDE5 inhibitors.
When used with an alpha blocker, hypotension (low blood pressure) may occur, but this effect does not occur if they are taken at least four hours apart.
