Medicines that block an enzyme called CYP3A4. Storage Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Common ones include: Flushing of the skin. Different brands may not work the same way. Kidney disease that needs to be treated with dialysis.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 . 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. Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor. PDE-5 is a protein in your body that breaks down the molecules that normally cause an erection. .