Sudden vision loss in one or both eyes can be a sign of a serious eye problem called non-arteritic anterior ischemic optic neuropathy NAION. This site is intended only for U. If you see air bubbles in the syringe, repeat the steps. 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. There is a problem with information submitted for this request. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its . Dosage for erectile dysfunction The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 . You may take it up to 4 hours before sexual activity. Do not take Viagra more than once per day. Shake the oral suspension (liquid) before you measure a dose. Use the dosing .