How Long Does It Take Vitamin B12 Injections to Work? 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 B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Alcohol and Vitamin B12 absorption: 5 things light to heavy drinkers should know How Quickly Do B12 Shots Work? Defy Medical