These pills were prescribed by my gastro... I did eat very light the two days before. I weigh 108lbs.. and the day before I did take 2/3 Dulcolax and then you take 12 (very large pills which I cut in half) and by 8:00 pm I was clear. My colonoscopy was scheduled for 3:00 pm the next day and I did not need to take the other 12 pills because my colon was clear. The pills are called Sutab. You can google it ... it's the easiest of all the preps I've had to do and since I'm 77 there will be no more.