How Long Do B12 Injections Last? Wow guys, you've been gate keeping!! Got my first B12 injection last week and it's like I am awake for the first time since having kids 20 years ago It's How to self inject intramuscular vitamin B12 Overview Guy's and St Thomas' NHS Foundation Trust B12 Shots in Friso, Sherman, Anna. and Sunnyvale, TX 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, How Long Does It Take Vitamin B12 Injections to Work?