Vitamin D: 300 IU in a drop

 

The issue is: where can I find the number of IU in a drop?

The answer is: not in the brochure that is in the box with the flask of Vitamin D...

It is a paradox of the heavily regulated healthcare system, you will not find the number of IU of vitamin D in a drop of the oral vitamin D solution. 
Consequently, you cannot personalise the dose you need in order to the "zone". Id est between 40 and 60 nanomoles per ml.