where do they inject b12 Best Vitamin Injection Site: Administering B12 Shots Vitamin B12 Injection Sites: All

This fear leads to a rigid adherence to a one-size-fits-all protocol, even when it is not clinically appropriate for the individual

Patients should monitor for severe abdominal pain, persistent vomiting, dehydration, or unexplained hypoglycemia and report these to their healthcare provider

A 1000 mcg intramuscular injection can leave serum B12 above the lab range for weeks, and I would not call that abnormal unless the clinical context disagrees

They also have an extensive list of restricted products

Long-term Storage in the Liver While the plasma half-life of vitamin B12 is relatively short, the liver can store vitamin B12 for much longer periods

PMID 20383582