My forehead isn't really flat to begin with, but the area between my eyebrows and both sides of my forehead were thin, so I got 5cc! At first, I thought it was ruined because it was so bumpy, but as the swelling gradually went down and settled down, it got better!! Of all the fillers I've had, it was the most painful, but it was bearable. For reference, I only applied anesthetic ointment before proceeding!