How Often Should You Take Vitamin B Complex Injections How Quickly Does a B12 Shot Work? Benefits & What to Expect Are you feeling run down? Low Energy? A quick Vitamin B12 injection can help support energy, metabolism, and overall wellness. It delivers the vitamin directly into the muscle, allowing your body to Taking Vitamin B12? Read this first. While B12 is often hailed as a safe energy and brain booster, many real users are reporting unexpected side effects including anxiety, insomnia,