It requires clinical trials, in-depth review of both the safety and efficacy of each drug, and continuous monitoring afterward
Nasal bioavailability differs significantly from injection bioavailability
There are some facial studies that are promising, but they are quite small and not designed to the strictest standards (by which we mean double blind, placebo controlled.) Another catch is that when it comes to facial anti-aging skin care stimulating hair growth is not really a good thing (unless of course, more facial hair is ok for you)
In fact, several scientific studies have noted a link between low vitamin B12 levels and obesity, metabolic disorders, and insulin resistance
However, your provider will adjust this amount based on your individual health profile and laboratory results