Imatinib, sold under the brand name Gleevec among others, is an oral chemotherapy medication used to treat cancer. Specifically, it is used for chronic myelogenous leukemia (CML) and acute lymphocytic leukemia (ALL) that are Philadelphia chromosome-positive (Ph+), certain types of gastrointestinal stromal tumors (GIST), hypereosinophilic syndrome (HES), chronic eosinophilic leukemia (CEL), systemic mastocytosis, and myelodysplastic syndrome. It is taken by mouth.Common side effects include vomiting, diarrhea, muscle pain, headache, and rash. Severe side effects may include fluid retention, gastrointestinal bleeding, bone marrow suppression, liver problems, and heart failure. Use during pregnancy may result in harm to the fetus. Imatinib works by stopping the Bcr-Abl tyrosine-kinase. This can slow growth or result in programmed cell death of certain types of cancer cells.Imatinib was approved for medical use in the United States in 2001. It is on the World Health Organization's List of Essential Medicines. A generic version became available in the UK as of 2017.