Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. 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. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. However, the dose is usually not more than 80 mg 3 times a day. This medication is taken with or without food an hour before sex.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or . VIAGRA usually starts to work within minutes. You may take it up to 4 hours before sexual activity. So there’s no need to rush. Eat smart before you start. VIAGRA can be . Yes, Viagra works to treat ED in most people. It increases blood flow to the penis to help you get or keep an erection. If Viagra doesn’t work for you, talk with .