May cause dose-related impairment of color discrimination. Use caution in retinitis pigmentosa. Sudden decrease or loss of hearing reported rarely. Hearing changes may be accompanied by tinnitus and dizziness. Decreases in blood pressure may occur due to vasodilator effects. Use with caution in left ventricular outflow obstruction (aortic stenosis or hypertrophic obstructive cardiomyopathy). May be more sensitive to hypotensive actions. Concurrent use with α-adrenergic antagonist therapy or substantial alcohol consumption may cause symptomatic hypotension. Painful erection >6 hours in duration, rare. Vision loss may occur rarely and be a sign of nonarteritic anterior ischemic optic neuropathy. Use not recommended in degenerative retinal disorders (e.g. retinitis pigmentosa). Use with caution in anatomical deformation of the penis (angulation, cavernosal fibrosis, or Peyronie’s disease), in bleeding disorders, and in hypotension (<90/50 mm Hg), uncontrolled hypertension (>170/100 mm Hg), heart failure within last 6 months, uncontrolled arrhythmias, stroke within last 6 months, MI within last 3 months. Use caution in left ventricular outflow obstruction (e.g. aortic stenosis). There is a degree of cardiac risk associated with sexual activity. Use with caution in patients who have conditions which may predispose them to priapism (sickle cell anemia, multiple myeloma, leukemia). Use with caution in hepatic and renal impairment, in active peptic ulcer disease, and in patients taking α-blockers (may cause hypotension), or strong CYP3A4 inhibitors. Concomitant use (regularly/intermittently) with all forms of nitrates contraindicated. Other treatments for erectile dysfunction use not recommended.