can b12 injections cause upset stomach Vitamin Deficiency & Nerve Problems : What You Must Know Understanding the B12 Vitamin Shot:

Oral or intraperitoneal administration of the product significantly reduces NNMT activity in solid tumor tissues, boosts intracellular NAD+ levels, inhibits rapid tumor cell proliferation, and cuts down tumor volume and weight without obvious damage to surrounding normal organs, indicating reliable high safety and precise targeting features

It is observed that in patients who are deficient in Vitamin B12, the CBC would show anemia, which manifests as a decrease in both hemoglobin and hematocrit

it works upstream, on an enzyme called nicotinamide N-methyltransferase (NNMT) that fat cells over-express when they become metabolically sluggish

Cox HD, Lopes F, Woldemariam GA, Becker JO, Parkin MC, Thomas A, Butch AW, Cowan DA, Thevis M, Bowers LD, Hoofnagle AN