Vitamin B12 supplements: forms, deficiency and labels

Vitamin B12 supplements are legal foods under US dietary-supplement law, not drugs, until someone claims they treat a disease. The structure/function line you can defend is narrow: the vitamin has a role in red blood cells and the nervous system. Saying a lozenge treats pernicious anemia, neuropathy or dementia is a disease claim. Injections and the nasal gel the NIH describes are prescription products.

The FDA disclaimer is not a quality mark

If a label makes a structure/function claim, it is supposed to carry the statement that the Food and Drug Administration has not evaluated the claim and that the product is not intended to diagnose, treat, cure or prevent any disease. The Federal Trade Commission still expects substantiation. The NIH fact sheet is the substantiation for the basic nutrient facts below. It is not substantiation for a brand's extra sentence about energy you will feel.

The forms, without a winner

Vitamin B12 is a group of compounds called cobalamins. The NIH Office of Dietary Supplements fact sheet says methylcobalamin and 5-deoxyadenosylcobalamin are the forms used in metabolism. Hydroxocobalamin and cyanocobalamin become active after the body converts them. Supplements are often cyanocobalamin. Methylcobalamin, adenosylcobalamin and hydroxocobalamin are also used. The same fact sheet says there is no evidence that absorption differs by form. At a dose under about 1–2 micrograms, absorption is about half, because intrinsic factor can still carry it. At 500 micrograms absorption is about 2%, and at 1,000 micrograms about 1.3%. A 1,000 microgram tablet is not 1,000 times more useful than a few micrograms from food. Most of it passes through.

Injections are a different product. The NIH fact sheet says cyanocobalamin and hydroxocobalamin can be given by injection as a prescription medicine, usually into muscle, when someone cannot absorb B12, including pernicious anemia. The NHS page on hydroxocobalamin says it is only available on prescription. NICE's clinical knowledge summary describes hydroxocobalamin 1 mg by intramuscular injection for deficiency that is not fixed by diet, and it also describes oral cyanocobalamin for diet-related deficiency. A shop tablet is not that injection. Clinics that sell B12 shots without a prescription relationship are outside what these pages describe.

Who is more likely to run short

The NIH fact sheet is blunt about food. Natural B12 is in animal foods. Vegans, who eat no animal products, and vegetarians who eat little, have a higher risk of deficiency unless they use fortified foods or a supplement. Breastfed infants of vegan mothers can become deficient early, and that deficiency can injure the developing nervous system. That is a reason for clinical care, not for a parent to guess a dose from this article.

Older adults are the other large group. Depending on the definition, the fact sheet cites deficiency rates in community-dwelling older adults from 3% to 43%, especially when atrophic gastritis reduces stomach acid and intrinsic factor. Pernicious anemia is an autoimmune cause of intrinsic-factor failure. People who have had stomach or intestinal surgery, and some people with coeliac disease, can also absorb too little.

Two common medicines interfere with absorption from food. The NIH fact sheet names proton pump inhibitors, such as omeprazole and lansoprazole, and H2 blockers, because they reduce stomach acid. It also names metformin, used for prediabetes and diabetes, as a drug that can lower serum B12. People on those medicines should ask the prescriber about monitoring. A high-strength shop tablet is not a substitute for that conversation, and it is not a reason to stop the medicine.

The US recommended dietary allowance for adults, from the same fact sheet, is 2.4 micrograms a day, 2.6 in pregnancy and 2.8 while lactating. The daily value used on US labels is 2.4 micrograms. The NHS treatment page does say that people who struggle to get B12 from diet, including vegan diets, may be advised to take tablets long term, and that diet-related deficiency may instead be treated with a hydroxocobalamin injection twice a year. Non-diet deficiency, once treated, is usually an injection every two to three months for life, with neurology cases referred to haematology.

What is established, and what the trials do not show

It is established that the body needs B12 to make red blood cells and to maintain the nervous system, and that deficiency can cause megaloblastic anemia and neurological symptoms, including numbness, which can occur without anemia. The NIH fact sheet says symptoms can take years to appear because the body stores about 1 to 5 milligrams. It is also established, in ordinary nutrition science, that people who do not eat animal foods need a fortified food or a supplement. Those are not marketing claims.

The authorized British wordings, as copied on the register compilation (described there as the register of 19 May 2026), include: vitamin B12 contributes to normal energy-yielding metabolism; to normal functioning of the nervous system; to normal homocysteine metabolism; to normal psychological function; to normal red blood cell formation; to the normal function of the immune system; to the reduction of tiredness and fatigue; and it has a role in the process of cell division. Each claim has a condition of use. The food has to be at least a source of vitamin B12. Check the register before relying on a paraphrase. A claim about tiredness is not a claim that a 1,000 microgram tablet treats chronic fatigue, and it is not a claim about mood disorder.

Cognitive decline is the tempting extra. The NIH fact sheet says observational studies disagree, and randomized trials have not shown that B12, alone or with folic acid and B6, improves cognition in older adults with or without dementia. That is a negative finding worth keeping. Energy claims on a label are the authorized nutrient wording, or a US structure/function line. They are not evidence that a person who is not deficient will feel different.

On treatment, the fact sheet summarises a 2018 Cochrane review of three small trials, 153 people, comparing 1,000–2,000 microgram oral doses with intramuscular B12. The evidence was low quality, and oral high doses normalised serum B12 about as well as injections in those trials. NICE still describes injections for people with neurological involvement and for many non-diet causes. High-dose oral B12 is a clinical option in that guidance, not a product to start without a clinician.

Safety and interactions

The NIH fact sheet says the Food and Nutrition Board did not set an upper limit, because of low toxicity, and that the body does not store an unlimited excess. That is not a dare to take the highest number in the shop. Folic acid can mask the blood picture of B12 deficiency while nerve damage continues. Metformin and acid-reducing drugs, already mentioned, are the interactions that change B12 status. Injections have their own side effects. The NHS hydroxocobalamin page lists pain at the injection site, nausea, diarrhoea, headache, dizziness, and rare anaphylaxis. Call 911 if you think you are having a severe allergic reaction after an injection. Shop tablets do not carry that injection risk. They also do not treat the causes that need an injection.

Call 911 in an emergency. Talk to a clinician licensed in your state before you use a 1,000 microgram tablet to replace prescribed injections, and before you stop metformin or a proton pump inhibitor. Oral high-dose B12 is discussed in the research the NIH summarises. Choosing it is a medical decision.

Labels on iHerb

Labels checked November 2026 on www.iherb.com. Jarrow showed a price. NOW showed supplement facts and a combo price for two products, which is not the lozenge price. Dollar figures are from www.iherb.com.