Hi: I have been drinking coffee for years about 3 cups daily. I have bad insomnia but always have the coffee before 10:00 am so it should be out of my system by then wouldn't you think? Anyhow on Sunday I wanted to see how I would sleep without the coffee so I went cold turkey. no coffee (well I had decaf) I had a headache.......all day! I still had a hard time sleeping that night. I decided to gradually cut down. I am mixing the regular coffee with the decafe 1:2. I will keep decreasing so eventually I will only be having decaf.