Elevated serum B12 is usually asymptomatic and discovered incidentally during routine blood tests Common causes include B12 supplementation, liver disease, haematological disorders, and chronic kidney disease Symptoms such as jaundice, unexplained weight loss, or bruising suggest underlying pathology requiring investigation B12 is water-soluble with no established upper safe limit, and excess is naturally excreted by the kidneys Management focuses on identifying and treating underlying causes rather than lowering B12 levels directly Patients with persistent elevation should undergo comprehensive assessment including liver function, renal function, and haematological investigations Table of Contents What Are the Symptoms of High Vitamin B12 Levels

It includes 1-5 intramuscular or subcutaneous injections of 1000 mcg crystalline cyanocobalamin daily, followed by oral doses of 1000-2000 mcg/day Parenteral administration should be reserved for those with significant neurological symptoms NICE guideline: Vitamin B 12 deficiency in over 16s: diagnosis and management: Malabsorption as the confirmed or suspected cause of vitamin B 12 deficiency: Offer replacement to people if: lifelong intramuscular vitamin B12 Autoimmune gastritis is the cause They have had a total gastrectomy They have had a complete terminal ileal resection If the person has a vitamin B 12 deficiency because of malabsorption that is not caused by autoimmune gastritis, or a total gastrectomy or complete terminal ileal resection (for example, malabsorption caused by coeliac disease, partial gastrectomy or some forms of bariatric surgery): Offer vitamin B 12 replacement and Consider intramuscular instead of

Use single-use needles and syringes only never share equipment between individuals
Storage: Refrigerate between 2C and 8C
13 Journal of Medicinal Chemistry (ACS)Bisubstrate inhibitors of NNMT with enhanced activity