Tadalafil remains in the body longer, as long as 36 hours in most cases, and thus has a longer window of opportunity. Sildenafil, however, has a shorter four- to six-hour active time frame. For men that want to be able to have intercourse at any time, Tadalafil might be the better choice. Tadalafil can also be taken daily. Sildenafil is prescribed for use as needed. This might be a better choice for individuals who are looking to plan a special occasion.