There is 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: anaphylaxis pulmonary edema congestive heart failure peripheral vascular thrombosis, which involves blood clots polycythemia vera, which is a type of blood cancer If anyone experiences difficulty breathing, hives, or swelling, they need emergency medical help
Current Pharmaceutical Design, 2014, 20(7):1121-1125 2.Sikiric P, Seiwerth S, Brcic L, Sever M, Klicek R, Radic B, Drmic D, Ilic S, Kolenc D
Alcohol Effect: Chronic alcohol use may reduce absorption and utilization of B vitamins
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Beyond that, the safety data comes from anecdotal reports in the peptide community