However, the dose is usually not more than 80 mg 3 times a day. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Finally, we checked customer reviews to better understand user experiences with each platform. Some illegal “street” drugs called “poppers” such as amyl nitrate, butyl nitrate, or nitrite. Patients should always ask their doctors for medical advice about adverse events. It continues to work for up to 4 hours, although its action is usually less after 2 hours. Teva sued to have the latter patent invalidated, but Pfizer prevailed in an August federal district court case.Key facts. 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.  · Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 hour.