Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension. It might work longer if you have mild to moderate erectile dysfunction. However, like any drug, it will not work for everyone, and some people may experience side effects. It does not work immediately, it takes about an hour to start working in the body. What is the difference between Viagra and Cialis? As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum . Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil . 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 .