Signs include: Hives or widespread rash beyond the injection site Swelling of face, lips, tongue, or throat Difficulty breathing or wheezing Rapid heartbeat Feeling faint or losing consciousness These symptoms require immediate medical attention
There is a risk of mild diarrhoea, upset stomach, nausea, a feeling of pain and warm sensation at the site of the injection, a feeling or a sense of being swollen over the entire body, headache and joint pain
Also, sadly enough, there also are many types of (chronic) diseases that require B12 injections, such as Pernicious Anemia, people with Crohns, celiac, and people with intestinal imbalances, such as intestinal tapeworms and excessive bacterial growth
Studied in models involving nicotinamide N-methyltransferase signaling, methylation-linked metabolism, and metabolic pathway regulation