How Dangerous Are High Vitamin B12 Levels? The People's Pharmacy Vitamin B12 Deficiency: Causes, Symptoms, and Treatment B12 Injection sites + How to use B12 Shots Safely Vitamin B12 overdose: Side effects of taking too many supplements; know when to stop Vitamin B12 (cobalamin) and folate (vitamin B9) are vitamins that serve important functions in the human body. Folate is needed for development and growth of cells (including red blood cells) and synthesis