Ive gained 18 ponds in just 5 months on Gleevec and it's driving me mad!!! I had surgery for GIST last Oct (2010)... 95%was removed & Gleevec is working well on what was left behind but not without weight gain,muscle ache, major fatigue, & blood counts stabilized after 1st month being hospitalized with neutrpenia, but the weight gain is absolutely,as said , driving me mad! I eat within calorie range of 1200 to 1600 and exercise 3 - 4 times week walking & running easy.