How Quickly Does B12 Shot Work? Does It Help to Lose Weight? Vitamin B12 Injections Basingstoke Wizard Clinics Vitamin B 12 Injection for Animals, 3000 mcg mL, 100 mL Vial Prescription Medication for Pets Vitamin B12 Injection 1500 mcg ml (10 x 2ml Vial) at 350 piece in Nagpur Vitamin B12 shots Prescription injections used to treat severe deficiency, pernicious anemia, or absorption issues (e.g., Crohn's, gastric bypass). They provide rapid, 100% absorption directly into the bloodstream, bypassing the digestive system.