Neurologist Dr. Sudhir Kumar warns that long-term use of common medications like Metformin, prescribed for diabetes and PCOS, can interfere with vitamin B12 absorption. This deficiency can develop silently, with early symptoms often overlooked, potentially leading to serious neurological damage. Vitamin B12 is crucial for nerve and blood cell health and DNA synthesis, and the body cannot produce it independently. Deficiency is common, particularly in older adults and vegetarians.