Vitamin B12 is found in many foods. Generally, when there is deficiency, it is due to a problem with absorption. For that reason, vitamin B12 deficiency is generally treated with injections. But it turns out that if the dosage is high enough, vitamin B12 can be taken orally. A review of research appearing in Family Practice News (November 15, 2004:59) shows that taking vitamin B12 orally may be as effective as getting by injection. The article reviewed four earlier studies that compared oral B12 supplementation with injections and placebos in patients with documented B12 deficiency. The studies showed taking a high dose orally (between one and two milligrams per day) is as effective as B12 injections. Lower doses were not as effective, in fact at 10 mcg per day, oral B12 supplementation is no more effective than placebo. Doctors in Sweden use oral B12 therapy instead of injections and have been getting good results for over 30 years.

  1. Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92(4):1191-1198. PubMed
    Takeaway: 2,000 µg/day oral cyanocobalamin corrected B12 deficiency as well as (and sometimes better than) a standard IM regimen over ~4 months.

  2. Bolaman Z, Kadikoylu G, Yukselen V, et al. Oral versus intramuscular cobalamin treatment in megaloblastic anemia due to cobalamin deficiency: a randomized study. Clin Ther. 2003. PubMed+1
    Takeaway: In megaloblastic anemia, high-dose oral B12 was as effective as IM injections for hematologic recovery—and was better tolerated and cheaper (90-day trial).

  3. Nyholm E, Turpin P, Swain D, et al. Oral vitamin B12 can change our practice. Postgrad Med J. 2003;79(930):218-220. PMC
    Takeaway: Primary-care patients maintained on 1,000 µg/day oral cyanocobalamin kept adequate levels after switching from injections—and preferred tablets.

  4. Nilsson M, Norberg B, Hultdin J, Westman G. Medical intelligence in Sweden. Vitamin B12: oral compared with parenteral? Postgrad Med J. 2005;81(953):191-193. PMC+1
    Takeaway: Sweden’s nationwide data (1990–2000) show widespread success using high-dose oral B12, with ~1,000,000 patient-years of oral therapy—supporting oral as a practical alternative to injections.

  5. Wang H, Li L, Qin LL, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018;3:CD004655. Cochrane Library+2Cochrane+2
    Takeaway: Across RCTs, 1–2 mg/day oral B12 produced similar normalization of B12 (and clinical outcomes) as IM therapy, often at lower cost.