Any site offering Viagra without a prescription is a scam! Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Without physical action to the penis, such as that occurring during sexual intercourse, sildenafil will not work to cause an erection. What special precautions should I follow? Luckily, there’s one foolproof way to tell when Viagra sold online is fake: If you don’t need a prescription for it, it’s fake. · Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents Medically reviewed .  · Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines . If you’re holding out for a generic version of branded Viagra, you won’t have to wait much longer. Teva Pharmaceuticals plans to release its generic of the “little blue .