Learn about the side effects of taking too much vitamin B12. ... Common side effects of vitamin B12 injections include mild diarrhea, itching, nausea and vomiting, dizziness, ...

Vitamin B12 deficiency causes symptoms like fatigue, sore tongue, constipation, and confusion. B12 deficiency is caused by a lack of dietary B12 or pernicious anemia, which affects B12 absorption. To ...