Imatinib is an active drug that’s available as a generic medication. It belongs to a group of drugs called tyrosine kinase inhibitors. It is used to treat blood cancer and gastrointestinal stromal tumors. It works by reducing or preventing the cancer cells from multiplying. Imatinib may also be used to treat immune system illnesses such as aggressive systemic mastocytosis and hypereosinophilic syndrome. Imatinib oral pills have been linked to mild side effects such as diarrhea, edema in the ankles, arms, legs, face, or other regions, indigestion, and headache.