While vitamin B12 naturally occurs in the body, making allergic reactions to it exceedingly rare, certain additives or preservatives in some preparations could cause mild localized reactions, such as redness or itching
What Happens in a Vitamin B12 Deficiency
GLP-1R is present not only in -cells and -cells, but also in -cells
L-carnitine uptake into primary rat cortical cultures: interaction with GABA
Its very plausible that a doctors concern regarding potential B12 toxicity may arise from the fact that elevated levels of B12 often indicate a serious underlying condition
Hensley K, Benaksas EJ, Bolli R, Comp P, Grammas P, Hamdheydari L et al