While there aren't very many side effects of too much vitamin B12 to be concerned with, there are a few things you
should be on the lookout for if you
are supplementing vitamin B12.
rare cases, excess B12 supplementation may cause some numbness or tingling in the arm, hands and face.
•Excess vitamin B12 may contribute to anxiety symptoms such as panic attacks.
•Too much vitamin B12 may contribute to or cause insomnia.