Different brands may not work the same way. Click here for an email preview. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. However, the dose is usually not more than 80 mg 3 times a day. However the dose is usually not more than 40 mg 3 times a day.He or she will tell you how much VIAGRA to take and when to take it. Get into the mood. You will not get an erection just by taking VIAGRA. You must be sexually stimulated for it to work. Take your time. VIAGRA usually starts to work within minutes. You may take it up to 4 hours before sexual activity.  · 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 this enzyme works. Viagra Coupons, Prices, and Savings Card. Generic Names: Sildenafil Citrate. Brand Names: Revatio. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about Viagra oral. 1. This is a generic drug. Even if this drug is covered by Medicare or your insurance, we recommend you compare prices.