The most common potential side effects when using<unk>  are headache, stomach discomfort or pain, indigestion, burping, acid reflux, back pain, muscle aches, flushing, and stuffy and runny nose. These side effects reflect the ability of PDE5 inhibition to cause vasodilation (cause blood vessels to widen), and usually resolve after a few hours. Back pain and muscle aches can occur 12 to 24 hours after taking the drug, and these symptoms usually resolve within 48 hours of onset. Vision In May 2005, the US Food and Drug Administration (FDA) found that<unk>  (along with other PDE5 inhibitors) was associated with vision impairment related to NAION (non-arteritic anterior ischemic optic neuropathy). Most, but not all, of these patients had underlying anatomic or vascular risk factors for development of NAION, unrelated to PDE5 use. The FDA concluded that they were not able to draw a cause and effect relationship, only an association; the label of all three PDE5 inhibitors was changed to alert clinicians to that fact. A 2019 meta-analysis found that<unk>  exposure was not associated with NAION. Hearing In October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including<unk> , requires a more prominent warning of the potential risk of sudden hearing loss as the result of post-marketing reports of temporary deafness associated with use of PDE5 inhibitors.
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