Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. This leads to more blood flow to the penis, leading to stronger erections. Men with the most severe erectile dysfunction saw the greatest benefit. Nitric oxide is a substance that causes blood vessels to relax.Viagra is available in three strengths: 25 milligrams (mg), 50 mg, and mg. What are the typical dosages of Viagra? Typically, your doctor will start you on the recommended dosage. Then. Does Viagra’s average price vary based on which strength I take (25 mg, 50 mg, mg)? It’s possible for Viagra’s cost to vary by a few dollars based on the strength you take. Other factors. Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online.