Vitamin B12 after gastric bypass Many guidelines recommend vitamin B12 injections in those with gastric bypass surgery. This study reviewed the efficacy and to see if oral B12 is adequate (1). The authors examined medical databases and obtained 19 articles to review. The results showed that oral vitamin B12 at doses of less than 15 mcg are insufficient to prevent deficiency in bypass patients. Higher supplementation doses showed better results, and in particular, doses of 1000mcg per day lead to an increase in B12 levels and was sufficient for prevention of deficiency. The authors conclude it’s best to utilize this dose after gastric bypass surgery to help prevent deficiency.