Remove the cap by pushing it down and twisting it counter-clockwise. Do not take more or less of it or take it more often than prescribed by your doctor. The primary endpoint was time to limiting angina in the evaluable cohort. If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on an average dose of sildenafil and increase or decrease your dose depending on your response to the medication. It continues to work for up to 4 hours, although its action is usually less after 2 hours.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 sexual activity. It can be taken  · 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 .  · 25 milligrams (mg) 50 mg; mg; Typical dosages. The following information describes commonly recommended dosages for ED. However, be sure to take the dosage your doctor prescribes for.