The appropriate dose depends on factors like age, kidney or liver problems, and other medications being taken. While generally considered safe, Viagra can cause side effects, including. Swallow a 50 mg dose of Viagra 30-60 minutes before sex. Your doctor may tell you to take slightly more or less, but do not take more than 100 mg at any one time. Also, do not take Viagra more than once a day. For best results, eat a low-fat meal before taking the Viagra. Talk to your doctor. When sildenafil is used for ED, it is used as needed, so you are not likely to miss a dose. If you are taking sildenafil for PAH and you miss a dose, take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. For erectile dysfunction, sildenafil should be taken as needed approximately 30-60 minutes before sexual activity, not exceeding once daily, while for pulmonary arterial hypertension, sildenafil must be administered three times daily at doses of 20 mg taken 4-6 hours apart. 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 minutes to 4 hours before sexual activity. Brand and Other Names: Viagra, Revatio, more. Viagra or Vibrique. Indicated for erectile dysfunction. 50 mg PO ~1 hr before sexual activity; however, may be taken anywhere from 30 min to 4 hr. How should I take Viagra? Take Viagra exactly as it was prescribed for you. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended. Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. Learn about the dosage of Viagra for erectile dysfunction (ED). You can also find information on the drug’s strengths, how to take it, and more. The typical starting dose for sildenafil in treating erectile dysfunction is 50 mg taken about one hour before sexual activity. Depending on effectiveness and tolerance, the dose can be adjusted to 25 mg or increased to a maximum of 100 mg. Sildenafil (Viagra) is a prescription medication that is usually prescribed in 25 mg, 50 mg, or 100 mg doses. Exceeding the dosage of sildenafil prescribed by your healthcare provider or taking it more than once within a 24-hour period can be considered too much sildenafil.