Vitamin B12 Injection Side Effects and Safety Heres what to expect when you come in for a B12 Injection , Well draw up your injection with you, clean and sterilize the injection site, communicate to make sure the injection is the most Feeling tired, foggy, or run down? It could be a B12 deficiency Weekly B12 injections help support: Increased energy + reduced fatigue Sharper focus + better mood Boosted What Happens If You Inject B12 Wrong: 6 Red Flags