Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are serious, life changing blood cancers. Patients with MDS and AML commonly experience complications related to bleeding, which affect patient quality-of-life and can sometimes lead to hospitalization or death. The investigators will conduct a randomized controlled trial to evaluate the effectiveness and safety of tranexamic acid (TXA; a medication that prevents clots from dissolving) to prevent bleeding. In this study, 50% of patients will be randomized (like the flip of a coin) to receive TXA; the other 50% of patients will receive placebo. The investigators will monitor both groups of patients to see if the medication improves the risk and/or severity of bleeding. If tranexamic acid were to safely reduced the frequency of bleeding, this would broadly influence how doctors provide care for patients with MDS and AML around the world.