Children 1 year of age and older weighing 45 kilograms kg or more—20 mg 3 times a day. However the dose is usually not more than 40 mg 3 times a day. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day. Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. Different brands may not work the same way.In so doing, Viagra lowers the systolic blood pressure (the “top” number in blood pressure measurements) by an average of 8 mmHg. For most people with heart disease, including . 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 . Do not take sildenafil if you are also taking a nitrate drug (such as nitroglycerin or isosorbide dinitrate/mononitrate) for chest pain or heart problems. Do not take sildenafil .