Has anyone else experienced muscle pain and stiffness on Ibrutinib? I started it as frontline treatment back in October and have been sailing along without any problems. Once or twice when my water intake was not adequate I did get cramping. Now, even with increased hydration I am getting cramps and stiffness in several muscles around my legs and hips. I'm wondering if it is a side effect of the medication, or related to my previous back problems.