John’s wort. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Sildenafil is also sometimes used to treat pulmonary hypertension high blood pressure in the blood vessels that supply the lungs. This medicine is available on prescription and you can also buy it from most pharmacies. This product is available in the following dosage forms: Tablet Suspension There is a problem with information submitted for this request.Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may.  · 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. How much does Viagra cost with insurance vs. without insurance? The Viagra prescription price can vary and depends on several factors. One factor is your insurance coverage.