List of products in the National Drug Code with proprietary name . This medication is used to treat certain cancers (such as mantle cell or marginal zone lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, Waldenstrom's macroglobulinemia). Ibrutinib belongs to a class of drugs known as kinase inhibitors. It works by slowing or stopping the growth of cancer cells. Ibrutinib is also used to treat a certain problem that may occur after a stem cell transplant (chronic graft versus host disease). It works by weakening your body's defense system (immune system).