Vitamin B12: Overdose and Side Effects Vitamin B12 toxicity: Diarrhoea, dizziness or nausea may be side effects to be aware of Express.co.uk 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 Why Do I Feel Worse After My B12 Injection? Causes & Management Bolt Pharmacy Vitamin B12 Injections for Aging and Longevity InVita Wellness Vitamin B12 Injection Side Effects and Safety