Hypersensitivity. Concomitant w/ nitrates, amyl nitrite. Severe heart or liver problem. Recent stroke or heart attack. Low BP. Retinitis pigmentosa. Loss of vision due to non-arteritic anterior ischaemic optic neuropathy. Childn <18 yr.
Sickle cell anaemia, leukaemia, multiple myeloma, Peyronie's disease, cardiac disease, stomach ulcer, bleeding disorder. Discontinue if sudden decrease or loss of vision. Renal or hepatic impairment. May affect ability to drive or operate machinery.