Do not mix the liquid with other medications or add anything to flavor the medication. Ask your healthcare professional how you should dispose of any medicine you do not use. Do not use more of it and do not use it more often than your doctor ordered. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup.Prices for Sildenafil (Revatio) are as low as $ with a GoodRx coupon. 6 hours. Taking it more frequently can raise your risk of side effects. There is usually no benefit to taking more than 20 mg 3 times a day, though some medical specialists will recommend higher strengths (still taken 3 times a day). White Round R And 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 . Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP.