Protocols › Vitamin B12

Vitamin B12 for a low B12 level

Goal: To bring a low vitamin B12 level back to normal, with tablets or injections as trials gave them.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Updated 3 Nov 2026
Dose

1,000 to 2,000 µg a day by mouth in the trials of a 2018 Cochrane review.[1] NICE advises at least 1 mg (1,000 µg) a day by mouth when the gut absorbs B12 poorly.[2]

Form

Cyanocobalamin by mouth in a 1998 trial.[3] NICE lists cyanocobalamin, methylcobalamin and adenosylcobalamin for supplements.[2]

How long

3 to 4 months in the trials.[1] Lifelong injections when the cause cannot be reversed, such as autoimmune gastritis.[2]

What studies found

A 2018 Cochrane review of 3 trials with 153 people: tablets brought blood B12 back to normal about as well as injections, with low-quality evidence.[1] A 2024 review of 13 studies with 4,275 patients found no significant difference between tablets, tablets under the tongue and injections.[4] In a trial of 38 people, 2,000 µg a day by mouth corrected blood counts and nerve problems as fast as injections.[3]

Ask a doctor first

The blood test comes first, because a supplement can raise the result without fully treating a deficiency.[2] When anemia comes with nerve problems, NICE says that treatment should not wait for the test results.[2] NICE advises lifelong injections for people with autoimmune gastritis or whose whole stomach was removed.[2] Metformin, proton pump inhibitors and H2 blockers can lower B12.[5] Ask a doctor or pharmacist before starting, and again if symptoms have not improved after 3 months.[2]

References

  1. Oral vitamin B(12) versus intramuscular vitamin B(12) for vitamin B(12) deficiency. Wang H, Li L, Qin LL, Song Y, Vidal-Alaball J, Liu TH Cochrane Database Syst Rev, 2018. PMID 29543316
  2. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). National Institute for Health and Care Excellence (NICE), 2024. www.nice.org.uk
  3. Effective treatment of cobalamin deficiency with oral cobalamin. Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J Blood, 1998. PMID 9694707
  4. Efficacy of different routes of vitamin B12 supplementation for the treatment of patients with vitamin B12 deficiency: A systematic review and network meta-analysis. Abdelwahab OA, Abdelaziz A, Diab S, Khazragy A, Elboraay T, Fayad T, et al. Ir J Med Sci, 2024. PMID 38231320
  5. Vitamin B12: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov