How Long Do B12 Injections Last? How Long Do the Benefits of Vitamin B12 Injections Last? Injection is a technique for delivering drugs by parenteral administration, that is, administration via a route other than through the digestive tract. Parenteral injection includes subcutaneous, intramuscular, intravenous, intraperitoneal Vitamin B 12 Injections B12 Shots Cincinnati Vitamin B12 absorption pathways and main factors and organs involved: Download Scientific Diagram Subcutaneous vitamin B12 administration using a portable infusion pump in cobalamin related remethylation disorders: a gentle and easy to use alternative to intramuscular injections Orphanet Journal of Rare Diseases Springer Nature