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 Vitamin B12 Injection: Benefits, Uses and Who Needs It Periville Pharmacy B12 Injections: How They Work and Who Needs Them Meo Nutrition How Quickly Does a B12 Injection Work? Timeline and Expectations Bolt Pharmacy Vitamin B12 is essential for energy production, nervous system function, and red blood cell formation. However, oral B12 supplementation doesn't work well for everyoneabsorption can be limited by digestive issues, certain medications,