Pharmacy Clinical Pearl of the Day: Long-Term Metformin Use and Vitamin B12 Deficiency


Patients on metformin should check their vitamin B12 levels on regular basis to make sure it is at normal range.

Clinical Pearl of the Day:

Long term use of metformin can cause vitamin B12 deficiency.


  • The mechanism by which metformin reduces the vitamin B12 levels is still unknown, but the most likely hypothesis is that metformin interferes with the calcium-dependent membrane action responsible for vitamin B12 intrinsic factor absorption, which occurs in the terminal ileum.
  • Patients on metformin should check their B12 levels on regular basis, possibly annually, to make sure it is within a normal range.
  • The normal level of vitamin B12 in the bloodstream is generally between 190 and 950 picograms per milliliter (pg/ml)

Reference: Association between metformin dose and vitamin B12 deficiency in patients with type 2 diabetes (

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