Like many others with CFS/ME or lyme i don't tolerate vitamin D very well. I've tried many different brands at different dosages without much luck. One way to raise vit. D is by using a megadose once weekly. I did so in the past for 6 weeks @ 50.000 IU as prescribed by my gastroenterologist. That raised my vit. D level from 21 to 47, yes i felt sick when taking the supplement but that was only for a single day. Given the success i had with such a weekly high dose i'm planning to try it again. Does anyone know if it's harmful to use a single dose of 50.000 IU weekly for a longer period of time?