Greater Glasgow and Clyde Medicines

Treatment of Vitamin B12 Deficiency in Adults

GGC guidance on the Treatment of Vitamin B12 Deficiency in Adults is available here (on StaffNet).  The guideline includes information on:

  • When to measure and also when not to measure vitamin B12
  • How frequently to measure vitamin B12
  • How to correct vitamin B12 deficiency
  • Common causes of vitamin B12 deficiency

Key messages

  • B12 should not be measured routinely in the following circumstances: tiredness, for routine haematological screen, in females taking progesterones, combined oral contraceptives and pregnancy
  • Not all patients with low B12 levels in serum have true B12 deficiency as low levels in serum do not always reflect reduced supply of B12 to the tissues
  • Oral cyanocobalamin is on the GGC Formulary, however, use is restricted to a 4 week trial on Acute prescription as a screening test for causes of vitamin B12 deficiency that are reversible with oral replacement (see Appendix 2 flowchart on last page of the guideline)
  • Proven vitamin B12 deficiency of dietary origin should be corrected by dietary adjustment. Foodstuffs rich in B12 include meat, liver, bovril, fish, cereals, eggs, cheese, fortified tofu and milk. Refer to the vegan society website for advice on maintaining adequate vitamin B12 levels on a vegan diet
  • IM hydroxocobalamin is recommended for confirmed pernicious anaemia and other causes of vitamin B12 deficiency that do not correct with a trial of oral B12 replacement

Vitamin B12 deficiency - as defined by serum vitamin B12 levels below the reference range on two separate occasions a month apart - is a common finding; however the identification of significant pathology either underlying or secondary to this deficiency is not. Vitamin B12 deficiency predominantly affects older adults and can take years to manifest as the body has significant stores.  Patients who have vitamin B12 deficiency may have symptoms of megaloblastic anaemia plus or minus unexplained neurological symptoms e.g. paraesthesia, numbness, cognitive changes, or visual disturbance.

Refer to the full guideline and PIL for further information.


Originally published 26/08/19 and updated on 06/08/21 with links to updated guideline. Medicines Update blogs are correct at the time of publication.