Hi Nancy, I have been on Chantix since Jan. and smoke free since beginning of Feb. Initially, i would have to say, I had no energy and had headaches, but nothing severe. I also felt down, but it went away quickly and I will be taking it for 6 months. The longer u are on it, the better chance u have of being smoke free. I do have a lot of gas.........lol. Now, do not worry about how long u take Chantix before u quit, cause I took it for a while before I quit. It is ok. You might just want to check with your doc to see if how u are feeling is ok. Take care and keep me posted as to how u are doing. Good Luck, you can do it!!