Diving deep into the query, Feeling Worse After a B12 Injection: Is it Normal ! provides insights grounded in science
After having a B12 shot, a person should monitor for adverse symptoms and seek medical help if they experience: severe pain at the injection site mild diarrhea a swelling sensation in the body temporary itching of the skin In rare cases, a person may also be at risk of: pulmonary edema peripheral vascular thrombosis, which involves blood clots polycythemia vera, which is a type of blood cancer If anyone experiences difficulty breathing, hives, and swelling, they need emergency medical help
Heres how they work and who theyre for
Therapeutics 33 (3), 358371.e2
Though uncommon, vitamin B12 may sting a little on injection, though this is usually a short-lived side effect