Medicare Part B Outpatient Coverage What Does Medicare Part B Cover Does Your Medicare Plan Cover B12 Shots? Medicare and B12 injections: Are They Covered? Does Medicare A and B Cover Prescriptions? Boomer Benefits Will Medicare cover checking vitamin D and B12 levels at the same time? 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