B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Deltoid Muscle Injection , The deltoid muscle is a common site for intramuscular (IM) injections, especially vaccines! , What gauge needle do you use for an IM injection? Answer in the comments!, Figure. Subcutaneous injection into the deltoid area The Australian Immunisation Handbook Optimal B12 Injection Sites for Maximum Absorption and Benefits Your Health Magazine