How to Give B12 Injections at Home to Yourself PA Relief How Quickly Does a B12 Shot Work? What to Expect 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, B12 Shots for Energy: Do They Work, Who Needs Them & What to Expect Greenwich Medical Spa The B12 Shot: What Every Human Needs to Know About Injectable Vitamin B12