Viagra (sildenafil) does not cure erectile dysfunction, but treats it, helping the patient to achieve a firmer erection and successfully complete sexual intercourse. Viagra comes in three doses - 25 mg, 50 mg, and 100 mg. 50 mg is the most commonly prescribed dosage, but if you are older or have certain health problems your health care provider may decide to start you on a lower dose. It's very important to visit your doctor before taking Viagra for the first time, as your health condition, your age and other important factors can be evaluated only by a trained professional. Do not take Viagra just because someone recommended you to do so - make sure you are thoroughly examined and prescribed just the dosage you need to benefit from the treatment. If you think you need to have your dose adjusted visit your doctor before you change the dose.