This medicine has been approved in the United States to treat premenopausal females who have low sexual desire. The products discussed in this site may have different product labeling in different countries. Do not take a double dose to make up for a missed one. The pharmacokinetics of sildenafil are dose-proportional over the recommended dose range. It is not recommended for use in Australia.Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. AdFind the lowest available Sildenafil prices in your area. No sign-up required. Save now! Search & compare local Sildenafil prices. Save up to 80% on Sildenafil instantly! Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be.