Patients should always ask their doctors for medical advice about adverse events. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. An inherited eye disease that affects the retina.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’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity. Based on how well you respond to this . Stop using Viagra and get emergency medical help if you have sudden vision loss. Before taking this medicine. You should not use Viagra if you are allergic to sildenafil, or: .