Taking this form of Vitamin D produced the most noticeable change from taking a supplement that I have ever experienced. I took a D-Test in 2009 and my ug/l was 8 (normal range 30-80) I started supplementing with this, eventually got my levels up to normal and I have never since had the recurring depression and lethargy that haunted me for over two decades. I have previously tried Source Naturals Vitamin D pills without any noticeable results, though those were only 400 IU pills and and these are 2000 IU drops. I cannot speak highly enough about Vitamin D supplementation and especially my experience with Bio-D Mulsion Forte. The result was do drastic for me and such a relief, if I were wealthy I would purchase mass quantities of Vitamin D tests and hand them out to those in need who can't afford them.