While B12 is water-soluble with no established upper safe limit (according to NHS and EFSA guidance), this does not preclude the possibility of adverse reactions, particularly from injectable forms
Vitamin B12 injections may also benefit people with certain types of cancer, low levels of stomach acid, or alcohol withdrawal
For example, if a 10mg vial is diluted with 2mL of bacteriostatic water, the concentration is 5,000mcg/mL
Testing the organic acid, methylmalonic acid, provides a more accurate level of actual usable B12 in patients
Who should check with a provider first If you are pregnant, nursing, have kidney disease, or take medications that interact with B12 metabolism (such as metformin), discuss this with a provider before starting