how to give yourself a b12 injection in the arm Self-Inject Vitamin at Home Best Vitamin B12 Injection Sites:

Genetic Factors: Inherited conditions affecting B12 metabolism can lead to deficiency despite adequate dietary intake

limited robust data on efficacy

It is advisable to avoid valproic acid, as it can impair liver mitochondrial function and cause hepatotoxic, while carbamazepine and phenytoin can decrease vitamin B12 and folic acid levels, therefore, these drugs should be avoided whenever possible

Contraindications Vitamin B12 injection is contraindicated in pregnant and lactating women, liver disease, kidney disease, infection, iron deficiency, folic acid deficiency, the patient undergoing treatment that has a direct effect on bone marrow, an allergy to medication, vitamin, preservative or cobalt

That's a rule payers enforce through NCCI edits