How Soon Do You Feel Less Tired After a B12 Injection? Signs You May Be Deficient in Vitamin B12 and How Injections Help Imaan Pharmacy Werneth Vitamin B12 Injections: What You Need To Know Low energy? Brain fog? Constant fatigue? Your body might be asking for support and a Vitamin B12 injection can help you reset , Stop pushing through fatigue and start feeling like you again! , Book B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Feeling constantly tired, foggy, or run down? Vitamin B12 plays a key role in energy production and nervous system health and low levels can lead to fatigue, brain fog, and weakness.