B12 Injection Frequency: How Often Should You Get a B12 Shot? Liv Hospital Vitamin b1, b6, and b12 Injection: The Complete FAQ Guide In 2025 AIPAK ENGINEERING How Long Does a B12 Shot Last? How often should vitamin B12 injections be administered and how frequently should laboratory monitoring be performed? A little insight to the importance of the b12 injections. My client hadn't been feeling well & had some bloods done with her GP. The results identified a severe deficiency in b12.