It has been my experience that my head is clearer while on round when I take 400IU with each meal; however I need to make sure I have at least 800 IU in me when I start the round. I usually end up taking 1,600 IU on the first day and last day of the round. I take extra antioxidants, including selenium in the hours after the last dose of the round to help mop up mobilized heavy metals.