I just read an article saying that in order to get the same level of T3 by using only T4 , it takes 2 weeks . So , since we know that 25mcg of T3 will takes about a week to be really absorbed and used , you would need 100mcg of T4 but 2 weeks earlier ... Or more T4 (cuz t4 level goes up like a stairway would basicly ...)