See Doctor Now. mg of Sildenafil (Viagra) is the highest dose prescribed. Your doctor decides what treatment is best for you. Different dosages all work the same way and last .Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. There is a problem with information submitted for this request. Click here for an email preview. Different brands may not work the same way. Your doctor takes your specific needs into account and guides you on how and when to take your prescribed dosage. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. · For oral dosage forms (suspension or tablets): Adults—20 milligrams (mg) 3 times a day. Your doctor may adjust your dose as needed and tolerated. . Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in .If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise. Sildenafil Viagra comes in tablets and prescriptions are available in increments from 20 to mg doses. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Store mixed oral liquid in the refrigerator. Use only the brand of this medicine that your doctor prescribed. The most commonly prescribed Sildenafil Viagra dosage is 50mg.