i had that nasty flu for about two weeks. i was coughing like crazy it hurt my insides. couldn't stop coughing. came onto glp and looked at some coughing threads for help. someone suggested 10,000 units per day. since i tried everything else that did not work, i had nothing to lose trying the D3. So after two days of taking 5000 units in the morning and 5000 units in the evening(total 10,000 per day) i feel way better. just a bit of the hacking left. the mucus cleared up a day later. seems to work.