Mean sildenafil plasma concentrations measured after the administration of a single oral dose of mg to healthy male volunteers is depicted below: Figure 5: Mean Sildenafil Plasma Concentrations in Healthy Male Volunteers. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Sildenafil is also sometimes used to treat pulmonary hypertension high blood pressure in the blood vessels that supply the lungs. Take sildenafil as needed before sexual activity.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum . Still, if your doctor says it’s okay for you to use and you end up paying out-of-pocket, you can still get the generic for a lot less than Viagra. According to price-comparison site test1.ru Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision.