But do you know why the two names always come up together? If this is achieved then a license can be considered. This boosts blood flow and helps you get an erection from sexual activity. It works for up to 36 hours. When a manufacturer applies to produce a generic medicine, they have to demonstrate bioequivalence.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . While generic sildenafil and Viagra are equally safe and effective, the medications have one key difference: price. Viagra costs around $60–$70 per tablet. Generic sildenafil . Last updated on Uses. Warnings. Before taking. Dosage. Side effects. Interactions. FAQ. What is Viagra? Viagra relaxes muscles found in the walls of blood .