How Long Do B12 Injections Last? Vitamin B12 injections benefit those with deficiencies or absorption issues, offering: 1. Energy Boost: Converts food to energy, reducing fatigue. 2. Mood Improvement: Essential for serotonin, aiding depression and anxiety. 3. Brain Not all shots are the same here's a guide Injections are a fast, effective way to deliver medications, nutrients, and vaccines directly into the bodybut not all injections are the How Long Does A B12 Shot Last? Affecting Factors of B12 Injection How to Give Yourself Intramuscular (IM) Injections Patients & Families UW Health