This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist. 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. This includes prescription or nonprescription over-the-counter [OTC] medicines and herbal or vitamin supplements. For treatment of pulmonary arterial hypertension: For oral dosage forms suspension or tablets : Adults—20 milligrams mg 3 times a day. Such patients must not apply any out-of-pocket expenses incurred using this Savings Offer toward any government insurance benefit out-of-pocket spending calculations, such as Medicare Part D true out-of-pocket TrOOP costs You are responsible for reporting use of this Savings Offer to any private insurer, health plan, or other third party who pays for or reimburses any part of the prescription filled using this Savings Offer, as may be required. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse.You can take it 30 minutes to 4 hours before sexual activity. And you shouldn’t take more than one dose per day. After you try the mg dose, you can let your doctor know how your body responded.  · For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed. Take sildenafil at least 30 minutes, but no more than 4 hours, before sexual activity (1 hour before is the most effective). Do not take more than once daily. A high- fat meal may delay how quickly.