The Annals of Pharmacotherapy. 2009;43(3):519-527.

In some countries, vitamin D is listed in micrograms, and the relationship is as follows: 2.5 mcg (micrograms) = 100 IU. 5 mcg = 200 IU. 10 mcg = 400 IU. 15 mcg = 600 IU. 20 mcg = 800 IU.