why would someone need b12 injections What Are the Benefits of Vitamin Injections? The Truth About B12 Injections:

In addition to cognitive function and energy levels, B12 supplements have been associated with a range of other health benefits

Approximately 97% of the drug is eliminated by 5 halflives, while ~99% is eliminated by 7 half-lives

As a cofactor, cobalamins are essential for two cellular reactions: the mitochondrial methylmalonyl-CoA mutase conversion of methylmalonic acid (MMA) to succinate, which links lipid and carbohydrate metabolism, and the activation of methionine synthase, which is the rate-limiting step in the synthesis of methionine from homocysteine and 5-methyltetrahydrofolate

The right needle is chosen from your body size and injection site, not from a one-size-fits-all rule