This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Dosing The dose of this medicine will be different for different patients. About sildenafil Viagra Sildenafil is a medicine used to treat erection problems erectile dysfunction. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. If too much is used, the chance of side effects is increased. Storage Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is . Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure .