- When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate (nitroglycerin), sodium nitroprusside, amyl nitrite ("poppers")

-In men for whom sexual intercourse is inadvisable due to cardiovascular risk factors

- Severe hepatic impairment (decreased liver function)

- Severe impairment in renal function

- Hypotension (low blood pressure)

- Recent stroke or heart attack

- Hereditary degenerative retinal disorders (including genetic disorders of retinal phosphodiesterases)