If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. Your doctor can then make a prescription or explain why he or she cannot do that for you. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Viagra and other PDE5 inhibitors are short-term measures for treating your condition. If you do not have one yet, a primary care doctor can still give you a proper diagnosis. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. Viagra can help with this situation or in others if you need it.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 prescription . Tips for talking to your doctor about ED. If you’ve been having difficulty getting or sustaining erections, talk about it with your doctor. Such a conversation is never easy, but thanks in . By Ginger Skinner Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active ingredient in both .