Worm - did your friend give them too big a dose, maybe? Emily and I gave all of our rats a round of Ivermectin when we only had six, and we've never had any problems. It was also very effective, with all of the other measures like cleaning the cages as needed and things, of course. They're only supposed to get a dose about the size of a grain of rice, approximately, according tot heir size. Have you any idea how much your friend gave hers?