If you have a low vitamin B12 level, injections can go a long way toward improving your health and well being. But if your B12 level is normal, don't fall for claims that Do Vitamin B12 Injections Hurt B12 INJECTIONS Vitamin B12 is a nutrient that helps keep the body's nerve and blood cells healthy and helps make DNA, the genetic material in all cells. Vitamin B12 also helps How Quickly Do Vitamin B12 Injections Work? Prime Aesthetics How Long Does It Take Vitamin B12 Injections to Work?