Why Do I Feel Worse After My B12 Injection? Causes & Management Bolt Pharmacy Feeling worse after B12 Injection: Answering concerns. La Vie Med Spa Too Much Vitamin B12: Risks, Symptoms and When to Seek Help Bolt Pharmacy 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