Oral, Sublingual and Nasal Vitamin B12: Absorption and What Trials Compared

How B12 gets absorbed

A modelling study (a computer simulation, not a trial in people) describes absorption as depending on a protein called intrinsic factor at ordinary food amounts, with passive diffusion adding a small share at very large doses. [1] In that simulation, a single 1 mcg dose was about 83% absorbed, a 2 mcg dose about 63% and a 1000 mcg dose about 1%. [1] Treat those as model estimates. They explain why very large tablet amounts can still raise blood levels: a small fraction of a big number is still a meaningful amount.

MedlinePlus says people who are over 50, follow a vegetarian or vegan diet, or have had stomach or intestinal surgery such as weight loss surgery are among those more likely to be deficient. [2] The NHS adds that absorbing B12 gets harder with age. [3] See pernicious anemia and intrinsic factor for the condition in which intrinsic factor is missing.

The three routes

• Swallowed (tablets, capsules, fortified foods). The standard form for most supplements. The NHS says diet-related deficiency may be treated with daily tablets taken between meals. [4]
• Sublingual (dissolves under the tongue). MedlinePlus notes that B12 is available in a form that dissolves under the tongue. [2]
• Nasal. MedlinePlus says a prescription form can be given as a nasal gel. [2]

What the trials compared

1. Oral vs injection in deficiency

   Low quality

   A 2018 Cochrane review (three trials, treatment 3 to 4 months) found similar blood B12 results. [5] It found no trial reporting symptoms or quality of life. [5]

2. Oral, sublingual and injection together

   Promising but limited

   A 2025 meta-analysis of 16 studies (6,098 people) found no statistically significant difference between the three routes. [6] Heterogeneity was substantial and publication bias was possible. [6]

3. Sublingual vs swallowed B-complex

   Promising but limited

   A trial in 41 adults aged 50 to 80 with raised homocysteine found no significant difference between the two routes after six weeks. [7] Homocysteine is a blood marker, not a symptom. [7]

4. Nasal B12

   Insufficient evidence

   A 2024 trial of 60 older adults with deficiency compared two nasal schedules of 1000 mcg doses. It reported effective replenishing of blood levels, with no comparison against tablets. [8] A 2020 review said only a few preliminary studies of nasal B12 were available. [9]

5. Severe nerve symptoms

   Insufficient evidence

   A 2020 review said the effect of oral treatment with severe neurological manifestations has not yet been adequately documented. [9]

Findings from people with deficiency do not automatically apply to people with normal B12, and the reverse is also true. Study amounts above are what researchers used, not advice.

Lozenges, sprays and "better absorbed" claims

Proper evidence not found that any one form (lozenge, spray, gummy or drops) is better absorbed in healthy people with normal stomach function. We searched PubMed on 2026-10-23 for randomised trials comparing sublingual or nasal B12 products with tablets in adults without deficiency. Claims on labels are marketing claims unless supported by a trial like those above. For the chemical forms, see B12 forms compared.