Answered 9/29/2014 by Samuel Grossman, BS Pharm, Pharm.D, CDE
Metformin works on reducing blood sugar by reducing the release of sugar from the liver and also prevents absorption of nutrients in the gut. Studies have shown that metformin can affect absorption of vitamins from food such as vitamin B12. In my practice, I recommend patients take vitamin B12 supplementation and also to space vitamin B12 supplementation apart from the dose of metformin. For example, metformin can be taken after breakfast and dinner and vitamin B 12 supplementation can be taken with lunch. Some patients prefer an injectable form of vitamin B12. In this case, you do not have to worry about an interaction with metformin. It is important to let your provider know that you are taking vitamin B12 supplementation and to monitor vitamin B12 levels at least once a year.