Pfizer Viagra (USA) 100mg / 50mg 30 Tablets Bottle Islamabad One tablet before sexual activity, not to exceed 1 tablet in any 24 hours. Viagra is taken about 20 minutes to a half-hour before you plan on becoming intimate with your partner. After your initial dose, the medication remains active in your system for several hours. Using oral medication to treat your ED allows for a very natural, spontaneous sexual response, alleviating. Therefore pressure and anxiety that both partners have likely experienced throughout your ED journey.