Cyanocobalamin (Vit B12) Injection for Pets VetRxDirect If you have been on Metformin for several years, monitoring is essential. The B12 Link: Long term use (typically 4+ years) can interfere with Vitamin B12 absorption. Symptoms to Watch: Fatigue, memory issues, How to Give a B12 Injection: Step By Step Instructions B12 Injection Wellness at Century City For those taking injectable B12, how often is your level tested? : r B12_Deficiency B12 Level Back Below "Normal" After Initial Set of Shots : r B12_Deficiency