Sudden vision loss in one or both eyes can be a sign of a serious eye problem called non-arteritic anterior ischemic optic neuropathy NAION. Take sildenafil exactly as directed. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph.Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may. Sildenafil, also known as generic Viagra, is the primary ingredient used in Viagra and works to treat ED symptoms in the same way. While brand name Viagra is slightly different than sildenafil.  · Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Do not take Viagra more than once per day. Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon). Viagra can help you have an erection when sexual .