How Long Do the Benefits of Vitamin B12 Injections Last? What Are B12 Injections? And Are They Safe? OmegaQuant Vitamin B D B12 Injections Near Ne Wilmington Urgent Care Clinic Wilmington Urgent Care And Family Clinic Vitamin B12 Injections: What You Need To Know Question of the Day:, How long does it take for a B12 injection to rev up the engines of energy? , For many people, the boost can be felt within 2448 hours. Others may notice gradual changes