Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa an inherited eye condition that causes loss of vision or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see. Take sildenafil exactly as directed. For sildenafil to work properly, you’ll need to be sexually excited. Take sildenafil as needed before sexual activity. If you take too much Taking too much sildenafil can cause unpleasant side effects.You can buy sildenafil citrate at the discounted price of $ by using the MDRx coupon, a savings of 43%. Even if this drug is covered by Medicare or your insurance, . Available strengths: 25 mg, 50 mg, mg Viagra comes in these strengths: 25 milligram (mg), 50 mg, and mg. Other forms of sildenafil (the active drug in Viagra) comes in other strengths. Strengths: 25 mg, 50 mg, mg; Brand: Viagra. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Adult dosage (ages 18–64 years) Typical dosage: 50 mg, taken as needed about 1 hour before.