I am deficient in Vitamin D and my endo told my doc to prescribe vitamin D which she did. She prescribed me ergocalciferol which is vitamin D2. My vitamin D levels are rising but very slowly. As per usual, I am researching my condition, because of the lousy Docs and have come across several articles suggesting that D3 is the better vitamin D to take. I've read that it can boost your levels up to 500 times faster than D2??? Also, D3 is more natural to our bodies as this is what our bodies make when exposed to sun. So, why do we get prescribed vitamin D2 and not D3? When we are tested for vitamin D, how do we know which one we are deficient in or doesn't it matter?? Found this article which was very interesting. Now wondering wether to take an over the counter D 3 too?