Revisiting Metformin: Annual Vitamin B12 Supplementation may become Mandatory with Long-Term Metformin Use

Monitoring of adverse drug reactions of a drug is a continuous process and runs through-out the life of a drug. Many rare adverse effects of a drug are documented after years of use; when a single case (signal generation) is reported leading subsequently to reporting of more cases. Deficiency of Vitamin B12 (vit B12) is a known sequel of prolonged metformin therapy. It was recommended to have annual measurement of serum vit B12 levels in patients on long term metformin therapy way back in 1970 itself. After more than 50 years of use of metformin, we have come to know that metformin induced vit B12 deficiency can cause neuropathy; forcing to change the recommendation from annual screening of vit B12 levels to annual supplementation of vit B12.