B-12 is a water soluble vitamin, which basically means if your body gets too much, then you just pee out the excess. If won't harm you if you have too much of it, only if you have too little. Now there are some vitamins like vitamin D that are fat soluble which means if you have too much, it gets absorbed into fat cells and can cause major issues, but B12 isn't going to hurt you if you have to much.