What Are the Symptoms of Erectile Dysfunction? Make sure to get an estimate of when you can expect your prescription in the mail. Medical consultations were also taken into consideration, as PDE5 inhibitors require a valid prescription from a licensed medical provider. Here are some key factors to consider when deciding: Pricing: Know how much your monthly supply will cost with shipping and tax. Read our editorial process. They have the same benefits and risks as their brand-name counterparts.The generic name for Viagra is sildenafil. The drug also has another brand name: Revatio. It works by slowing down the action of PDE5, an enzyme in the blood vessel walls.. This enzyme breaks down. tingling in the arms, feet, legs, or hands. numbness in the arms, feet, legs, or hands. headache. diarrhea. heartburn. trouble differentiating between colors like blue and green. seeing a blue. Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision.