Medicines that block an enzyme called CYP3A4. Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. This boosts blood flow and helps you get an erection from sexual activity. This medication is taken with or without food an hour before sex. Some medications should not be taken with sildenafil.Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. 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 drug that’s used in adult males* with ED. With ED. If you’re holding out for a generic version of branded Viagra, you won’t have to wait much longer. Teva Pharmaceuticals plans to release its generic of the “little blue pill” as early as December.