B12 Shots for Weight Loss: What You Need to Know ISSA Comment b12 to get free ebooks. Vitamin B12 Injection Complete Dosage Guide, 1 Forms of B12 Used for Injection:, Methylcobalamin Active, brain + nerve repair form (best for long term use)., Question of the Day:, How long does it take for a B12 injection to rev up the engines of energy? , For many people, the boost can be felt within 2448 hours. Others may notice gradual changes How to self inject intramuscular vitamin B12 Overview Guy's and St Thomas' NHS Foundation Trust