It's over the counter here. I take two tablets...2000 IU per tablet a day. It promotes a healthy immune system, and, helps bone health too. I just found out today that I also need to be on something else for my bone health. Had a Dexa test. I will start taking Alendronate..70mg tab. once a month. So between the D-3 and that, maybe my bones will behave themselves. But I really like the D-3 for the immune system.