My doctor just gave me a prescription for 50,000 IU to be taken once per week. When I had my blook tested for Vitamin D the normal range is between 30 - 100 but I ranked at a mere 12. The 50,000 IU per week is not toxic and so far does not have any side effects. I have read that a deficiency in Vitamin D will also make you feel more fatigued and have joint/muscle pain. I am hoping this prescription helps with that.