metforminA study appearing in the Achieves of Internal Medicine (2006; 166(18): 1975-9) links metformin use (sold under the brand name Glucophage) to vitamin B12 deficiency. The subjects of the study were 155 subjects with both diabetes and vitamin B12 deficiency; they were compared to 310 matched controls. There was an association between metformin use and vitamin B12 deficiency; with the deficiency being proportional to both dosage and duration of metformin use. Average vitamin B12 levels in the diabetics was 148.6 pg/mL compared to 466.1 pg/mL in the group not using the drug. Increased use of the drug was associated with lower vitamin B12 levels. Patients taking metformin for three years had a 2.39 adjusted odds ratio of being vitamin B12 deficient.