Medical consultations were also taken into consideration, as PDE5 inhibitors require a valid prescription from a licensed medical provider. These are commonly prescribed for an enlarged prostate or male pattern baldness. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. We also looked at additional services, such as access to digital pharmacies and home delivery options. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. · What is sildenafil? Sildenafil relaxes muscles of the blood vessels and increases blood flow to particular areas of the body. Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. 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 . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or .