B12 under the tongue refers to sublingual vitamin B12 supplements designed to dissolve beneath the tongue. Whilst traditionally thought to be absorbed directly through oral mucous membranes, research indicates that much of the dose is swallowed and absorbed via the digestive system, similar to standard oral tablets. Sublingual B12 is available in cyanocobalamin or methylcobalamin forms and may suit individuals with certain digestive conditions or those who struggle to swallow tablets. However, for confirmed B12 deficiency—particularly pernicious anaemia or neurological symptoms—intramuscular hydroxocobalamin injections remain the first-line treatment in the UK, as recommended by NICE and the British Society for Haematology.

What Is Sublingual Vitamin B12 and How Does It Work?

Sublingual vitamin B12 refers to a formulation of cobalamin designed to dissolve under the tongue. While traditionally described as being absorbed directly through the mucous membranes in the mouth, research suggests that much of the dose is actually swallowed and absorbed through the digestive system via passive diffusion, similar to standard oral tablets.

Vitamin B12 (cobalamin) is an essential water-soluble vitamin crucial for red blood cell formation, neurological function, and DNA synthesis. The body cannot produce B12, so it must be obtained through diet (primarily animal products) or supplementation. Traditional oral B12 supplements rely on a complex absorption process involving gastric acid, intrinsic factor (a protein produced in the stomach), and specific receptors in the small intestine.

Sublingual formulations typically contain either cyanocobalamin or methylcobalamin. Cyanocobalamin is a synthetic form that the body converts to active forms, whilst methylcobalamin is one of the naturally occurring forms. When placed under the tongue, these tablets or lozenges dissolve within minutes.

The theoretical advantage of this delivery method is that it may help individuals with certain digestive issues, such as reduced stomach acid production or lack of intrinsic factor. However, evidence has not consistently demonstrated that sublingual B12 is superior to standard high-dose oral B12 tablets. Both routes can effectively raise serum B12 levels in many individuals, as high-dose oral B12 (1000-2000 micrograms) can be absorbed by passive diffusion even without intrinsic factor.

In the UK, hydroxocobalamin injections remain the preferred treatment for confirmed B12 deficiency, particularly for pernicious anaemia or when neurological symptoms are present.

Benefits of Taking B12 Under the Tongue

Sublingual B12 supplementation offers several potential advantages for specific groups of people. One proposed benefit is the partial bypass of the gastrointestinal absorption pathway, which can be compromised in various clinical scenarios. This may be relevant for people with malabsorption disorders such as Crohn's disease or coeliac disease, though it's important to note that for pernicious anaemia, intramuscular hydroxocobalamin injections remain the first-line treatment in the UK, as recommended by NICE and the British Society for Haematology.

Another advantage is convenience and ease of use. Sublingual tablets dissolve quickly without water, making them suitable for people who have difficulty swallowing conventional tablets or capsules. This can improve adherence, especially in elderly populations or those with dysphagia. The pleasant taste of many sublingual formulations (often cherry or berry flavoured) may also enhance compliance compared to standard supplements.

For individuals following a vegan or vegetarian diet, sublingual B12 provides an accessible way to prevent deficiency, as plant-based foods contain negligible amounts of bioavailable B12. Regular supplementation can help maintain adequate levels and prevent complications associated with deficiency, including megaloblastic anaemia, peripheral neuropathy, and cognitive impairment.

Some users report subjective improvement in energy levels with sublingual B12, though this may reflect placebo effects or the psychological benefit of a different administration route. It's important to understand that whilst sublingual and high-dose oral B12 supplements can both effectively raise B12 levels, neither has been proven to boost energy in people who are not deficient.

Who Should Consider Sublingual B12 Supplements?

Sublingual B12 supplementation may be appropriate for several specific patient groups. Individuals with confirmed B12 deficiency due to dietary insufficiency may benefit from oral B12 supplementation (including sublingual forms). However, it's important to note that for pernicious anaemia or deficiency with neurological involvement, intramuscular hydroxocobalamin injections remain the first-line treatment in the UK, as recommended by NICE and the British Society for Haematology.

Older adults may be at increased risk of B12 deficiency. Age-related changes include reduced gastric acid production (hypochlorhydria or achlorhydria), which impairs the release of B12 from food proteins. Additionally, atrophic gastritis, common in elderly populations, can reduce intrinsic factor production. The prevalence of B12 deficiency increases significantly after age 60, and correcting deficiency can help maintain normal neurological function. However, supplementation has not been shown to improve cognitive function in older adults who are not deficient.

People following strict vegan or vegetarian diets should consider regular B12 supplementation, as plant-based foods do not provide reliable sources of this vitamin. The Vegan Society and NHS recommend that vegans take B12 supplements or consume fortified foods regularly. Sublingual formulations are an option, though standard oral supplements are equally effective when taken in adequate doses.

Individuals with certain gastrointestinal conditions affecting absorption—including inflammatory bowel disease, coeliac disease, or those who have undergone bariatric surgery—may need B12 supplementation. For bariatric surgery patients, it's important to follow the specific protocols recommended by your surgical team, as many UK centres recommend routine intramuscular B12 after certain procedures such as Roux-en-Y gastric bypass.

People taking certain medications should discuss B12 monitoring with their GP. These include metformin (commonly prescribed for type 2 diabetes), which the MHRA advises may reduce B12 levels with long-term use, and proton pump inhibitors (used for acid reflux). Regular monitoring may be appropriate, especially if symptoms of deficiency develop.

How to Use Sublingual B12 Tablets Correctly

To use sublingual B12 supplements effectively:

• Place the tablet under your tongue (in the sublingual space) rather than on top of it.

• Allow it to dissolve completely without chewing or swallowing. This typically takes 1–3 minutes, depending on the formulation.

• Avoid eating or drinking for at least 5–10 minutes before and after taking the tablet to ensure optimal contact with the mucous membranes.

• Allow the tablet to dissolve fully before swallowing any saliva.

Dosage varies depending on the reason for supplementation. For prevention of deficiency in vegans or vegetarians, The Vegan Society recommends either 10 micrograms daily or 2000 micrograms weekly. Alternatively, adequate intake of B12-fortified foods can provide sufficient amounts.

For treatment of confirmed dietary B12 deficiency, oral cyanocobalamin at doses of 50-150 micrograms daily may be used. However, for pernicious anaemia or deficiency with neurological symptoms, intramuscular hydroxocobalamin is the recommended treatment in the UK. Initial treatment is typically followed by monitoring with a full blood count after 10-14 days to check for response, with further clinical review and blood tests at around 8 weeks.

Timing of administration is flexible, though some people prefer taking B12 in the morning. Consistency matters more than specific timing—establishing a daily routine improves adherence.

Storage is important: keep sublingual tablets in their original container, away from moisture and direct sunlight, as humidity can cause premature dissolution. Check expiry dates regularly.

If you are prescribed B12 injections by your GP for pernicious anaemia or neurological symptoms, do not substitute sublingual tablets without medical supervision. Intramuscular administration remains the gold standard for these conditions, as recommended by NICE and the British Society for Haematology.

Potential Side Effects and Safety Considerations

Sublingual vitamin B12 is generally considered very safe, as it is a water-soluble vitamin with minimal risk of toxicity. The body excretes excess B12, and no upper tolerable limit has been established by UK or European regulatory authorities. However, some individuals may experience mild side effects or should exercise caution in specific circumstances.

Common side effects are rare but may include:

• Mild gastrointestinal symptoms such as nausea or diarrhoea (though less common with sublingual than oral routes)

• Headache or dizziness in some users

• Skin reactions, including itching or rash, particularly in individuals sensitive to cobalt (a component of cobalamin)

Unlike some other B vitamins, oral B12 supplements rarely affect urine colour. However, hydroxocobalamin injections can cause a harmless pink or red discolouration of urine.

Very rarely, allergic reactions can occur. Seek immediate medical attention if you develop symptoms such as difficulty breathing, severe rash, or swelling of the face, lips, or throat. Report any suspected side effects to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Drug interactions are uncommon but worth noting. Chloramphenicol (an antibiotic) may reduce the haematological response to B12 therapy. If you are taking metformin, colchicine, or proton pump inhibitors long-term, discuss B12 monitoring with your GP, as these medications can affect B12 status over time.

Individuals with Leber's hereditary optic neuropathy should avoid cyanocobalamin formulations, as there is evidence suggesting potential harm; hydroxocobalamin is the preferred alternative and should be used under medical supervision.

When to contact your GP: If you suspect B12 deficiency (symptoms include persistent fatigue, pins and needles, memory problems, or pale skin), seek medical assessment before self-supplementing. Blood tests measuring serum B12 and full blood count are standard initial tests; intrinsic factor antibodies may be checked if pernicious anaemia is suspected. Do not rely solely on sublingual supplements if you have neurological symptoms—these require urgent medical evaluation and may necessitate intramuscular B12 therapy to prevent irreversible nerve damage.

Frequently Asked Questions