Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. It can be taken alongside PDE5 inhibitors such as Viagra but it may require monitoring. The hardening of blood vessels can prevent a good supply of blood from reaching the penis, in turn making erections difficult to achieve. Viagra can be used with caution by those with hypertension but the prescriber may wish to keep a check on blood pressure levels. Follow your doctor’s orders or the directions on the label.Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. The usual dose is 50mg, when you need it. Do not take it more than once a day. . 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 . You should not take Viagra if you don’t have ED. Sildenafil warnings How well you get on with Viagra can have a lot to do with other health conditions. You’ll want .