After finding out I have a vitamin d deficiency from my doctors I started taking this product. There are multiple levels of vitamin d but 5,000 seems to be the average. Within a couple weeks my levels were back up! This also stayed in my system for a bit, averaging a couple months, as when I had more bloodwork done my levels were too high! So once you know what dose is right for you, then it is amazing! I noticed I was much happier and less moody as vitamin d can play a role in your happiness and helps with depression.