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. The products discussed in this site may have different product labeling in different countries. Severe liver disease. Vardenafil usually works for 4 to 5 hours. You can take it in a small dose daily or in a larger dose as needed.Next steps Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile dysfunction. The cost of the drug with and without insurance can depend on several factors, such as . Prices for Sildenafil (Viagra) are as low as $ with a GoodRx coupon. (Viagra) per day, The list below does not include all possible drug interactions with Sildenafil .  · The cost of sildenafil without insurance starts at $* for a quantity of 30, 20mg tablets, using a RxSaver coupon. The cost of sildenafil can vary in price depending on the pharmacy your sildenafil prescription is filled at. Below is a list of pharmacies and the starting cost of a sildenafil prescription using an RxSaver coupon.