been using phen for about 6 mo. now and I love the stuff. I only use half tab on work out days and sometimes at wk when im dragging. ive taken it as late as 5pm and had no prob falling asleep by midnite and I had a pre-wkout at approx. 6pm. I have major tolerance for caffeine so that's prob why I have no sleep issues on it. I would def take a half tab early in the day and see how you react to it.