Why Do I Feel Worse After My B12 Injection? Causes & Management Bolt Pharmacy Fun Fact Friday! Ever wondered Why is my B12 injection red? All B12s are cobalamins they have a cobalt atom at the center of a special ring shaped molecule called A vitamin B12 deficiency can cause a range of symptoms, including some that appear in the mouth Vitamin B12 Deficiency: Signs & Symptoms Vitamin B12 is essential for nerve health, red blood cell formation, and brain function. When B12 levels are low, symptoms often develop slowly and silently, Vitamin B12 Injection Side Effects and Safety