Brand names Why is this medication prescribed? Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. How should this medicine be used? Common ones include: Flushing of the skin. If you ever need emergency medical treatment for a heart problem, the healthcare providers who treat you will need to know when you last took sildenafil. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men.Sildenafil is a generic drug, which is an exact copy of the active drug in a brand-name medication. The generic is considered to be as safe and effective as the original drug. And generics tend to. It depends on a few factors, including your age and why you’re taking it, since Viagra is not only used to treat ED. Your doctor will tell you how much you should take. For help with erections. The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity. And you.