Background/Objective <p>Metformin, the first-line therapy for type 2 diabetes, has been associated with both the development and amelioration of various types of anemia. Given diabetes’ global prevalence (affecting ~ 589 million adults) and metformin’s widespread use, understanding these hematological effects is crucial for patient management. This review highlights the need for individualized treatment strategies to balance metformin’s glycemic benefits with its hematologic risks.</p> Methods <p>This review examines the complex relationship between metformin use and anemia, synthesizing evidence from clinical and experimental studies.</p> Results <p>While metformin is linked to megaloblastic anemia (due to vitamin B12 deficiency) and hemolytic anemia, it may improve iron utilization in some cases and benefit Fanconi anemia, anemia of chronic disease (ACD), and sickle cell anemia (SCA). The mechanisms vary, including impaired B12 absorption, oxidative stress modulation, AMPK activation, and anti-inflammatory effects.</p> Conclusions <p>Conflicting data exist on iron deficiency anemia (IDA), with some studies suggesting metformin reduces iron absorption while others propose improved iron metabolism. Key recommendations include routine B12 monitoring for long-term metformin users and further research to clarify dose-dependent effects and therapeutic potential in nondiabetic anemia.</p>