What are vitamin B12 injections, and who are they for?

We did not find an FDA-approved methylcobalamin drug product for any use (checked September 27, 2026).

Why people use it

The UK's NICE guideline recommends lifelong B12 injections for autoimmune gastritis, which is sometimes called pernicious anemia, and suggests considering tablets first when diet is the cause.[4] NICE is a UK health body, so its guideline reflects UK practice and UK medicine licensing and is not US guidance. The UK's NICE guideline recommends lifelong B12 injections into a muscle when the deficiency is caused, or suspected to be caused, by autoimmune gastritis, or after surgery that removed the whole stomach or the whole end section of the small intestine. The UK's NICE guideline notes that autoimmune gastritis is sometimes called pernicious anemia, the term used on US B12 injection labels.

For other causes of poor B12 absorption, such as coeliac disease, partial removal of the stomach or some forms of weight-loss surgery, the UK's NICE guideline suggests considering injections into a muscle instead of tablets, and, if tablets are used, at least 1 mg (1,000 micrograms) a day.[4] When a medicine or recreational nitrous oxide use caused the deficiency, the UK's NICE guideline says either injections or tablets can be offered, based on clinical judgement and the person's preference. When diet is the cause, the UK's NICE guideline suggests considering B12 tablets, and injections instead if the person has a condition that may get worse quickly or if taking tablets regularly may be difficult. When the cause of deficiency is unclear and poor absorption is not suspected, the UK's NICE guideline suggests considering tablets rather than injections, and checking the response at the first follow-up visit. If symptoms still interfere with daily activities while a person is taking tablets at the highest licensed dose, the UK's NICE guideline says to switch to B12 injections into a muscle.

NIH's Office of Dietary Supplements says B12 deficiency is typically treated with injections because they bypass any barriers to absorption, but that high doses of oral B12 might also be effective.[5] NIH's Office of Dietary Supplements says B12 injections are typically used for deficiency caused by pernicious anemia and by other conditions that cause poor B12 absorption and severe deficiency.[5]

The cyanocobalamin injection labels say that for pernicious anemia, B12 injections are the recommended treatment and will be needed for the rest of the person's life. One cyanocobalamin injection label says that for pernicious anemia, "The oral form is not dependable."[2] The same label says oral absorption is considered too undependable to rely on in people with pernicious anemia or other conditions that cause poor B12 absorption.[2] For people whose gut absorbs B12 normally, the same label says that where oral treatment is not considered adequate, injections may be used at first, depending on how severe the deficiency is, and that long-term treatment should be with oral B12.[2]

The cyanocobalamin injection labels say that higher-than-normal B12 needs, for example in hemolytic anemia or in liver or kidney disease, can usually be met with oral B12. A 2014 British haematology guideline says oral B12 may be suitable as long as adequate doses are taken and taking them regularly is not a problem.[6]

The right form of B12 treatment depends on the cause of the deficiency, and a licensed clinician makes that decision.

Evidence: does treatment work, and what to expect

The cyanocobalamin injection labels describe checking blood counts during treatment to confirm that the anemia of B12 deficiency is responding. The UK's NICE guideline says B12 replacement treatment is effective in most people with a confirmed deficiency.[4] The UK's NICE guideline says the response to B12 treatment varies with the cause of the deficiency, that symptoms could start to improve within 2 weeks but this may take up to 3 months, and that symptoms can take much longer to go away completely. The UK's NICE guideline says B12 treatment should not be delayed while waiting for test results in people with suspected megaloblastic anemia and nerve symptoms.

Potential benefits

Evidence levels in this table follow our grading key: Established means consistent results from randomized trials or a review of them, and "as label and guideline content" means the rating covers only what the drug labels and guidelines say; Emerging means some controlled human evidence that falls short of that; Evidence against means trials tested the claim and did not find the effect; and "No support found" means the searches named in that row did not find a trial of the kind that row describes, and the row says what was found instead. That is a search result and does not mean that no trial exists. Each rating applies only to the people named in its row; the energy, memory and mood rows are about people without a clear B12 deficiency.

The cyanocobalamin injection and nasal spray labels we reviewed list uses related to vitamin B12 deficiency, not energy, weight loss, anti-aging or longevity (checked September 27, 2026). We did not find an FDA-approved methylcobalamin drug product for any use, including energy, weight loss, anti-aging or longevity (checked September 27, 2026).

Energy without a deficiency

NIH's Office of Dietary Supplements says B12 taken by mouth does not appear to improve athletic performance or endurance in people who have enough B12.[5] NIH's Office of Dietary Supplements notes that B12 is often promoted as an energy enhancer, but that it appears to have no benefit for performance when there is no nutritional deficit.

The three very small randomized, placebo-controlled trials of injections containing B12 for tiredness or fatigue that we found in PubMed searches on October 1, 2026 had mixed results: two found no difference from placebo, and a 1973 pilot found better well-being on hydroxocobalamin only in the people who received placebo first.[16][17][18] In a 2021 crossover trial of 20 professional singers without known or suspected B12 deficiency, a B12 injection made no meaningful difference to voice problems or voice fatigue compared with a salt-water placebo injection. In a 1989 trial of 15 people with chronic fatigue syndrome, injections combining liver extract, folic acid and cyanocobalamin showed no significant difference from placebo. A 1973 pilot trial of 28 people complaining of tiredness found better well-being with hydroxocobalamin injections only among people who received placebo first; people given hydroxocobalamin first showed no difference between the two treatments.

In an 8-week trial of 95 adults with irritable bowel syndrome or inflammatory bowel disease, disabling fatigue and normal B12 levels, high-dose B12 tablets did not reduce fatigue more than placebo.[19] The UK's NICE guideline lists unexplained fatigue among common symptoms of B12 deficiency, which does not show that B12 helps tiredness in people who are not deficient.[4]

The fatigue trials described here come from PubMed searches on September 28 and October 1, 2026 for randomized or placebo-controlled trials of B12 and fatigue, tiredness, energy, vitality or well-being; we did not search other databases or trial registries for this question.

Memory, thinking and mood

A 2021 review of 16 randomized trials in 6,276 people without advanced neurological disease or a clear B12 deficiency found no effect of B12, alone or with other B vitamins, on any area of memory or thinking.[3] The same review found no overall effect of B12, alone or with other B vitamins, on measures of depression.[3] The review's authors concluded that "Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders."[3] The review covered B12 in general, alone or with other B vitamins, and we did not check how many of its trials used injections.

NIH's Office of Dietary Supplements says randomized controlled trials have shown no improvement in cognitive function among older adults with or without dementia, mild cognitive impairment or Alzheimer's disease when they took B12 alone or with folic acid, vitamin B6 or both.[5]

Weight loss

In searches of PubMed, Europe PMC and ClinicalTrials.gov on October 1, 2026, we found no published result from a trial in people of B12 injections for weight loss. ClinicalTrials.gov lists one small randomized trial, completed in 2013, in which 22 adults with a body mass index of 30 to 40 and no B12 deficiency all took the same weight-loss medicine by mouth and got weekly injections of either B12 or salt water, with weight change as the main outcome. The trial is registered and has reported no results as of October 1, 2026: none are posted on its record, and we found no published report in PubMed or Europe PMC. The record names an individual investigator at East Carolina University as sponsor and was last updated on August 13, 2015.[7] A 2020 analysis of the B-PROOF trial, in which 2,919 people aged 65 and older with raised homocysteine took a daily tablet of folic acid plus B12 or placebo for 2 years, found no significant effect of the vitamins on changes in body mass index, fat mass or fat-free mass.[20][21] The trial was designed to study fractures and gave B12 by mouth together with folic acid, so it does not test B12 injections for weight loss. NIH's Office of Dietary Supplements lists weight loss among the possible effects of B12 deficiency and does not describe B12 as a weight-loss aid.[5]

The cyanocobalamin products whose labels we reviewed, an injection and a nasal spray, are FDA-approved only for vitamin B12 deficiency and related conditions listed on those labels, not for energy, weight loss or 'lipotropic' programs. Using cyanocobalamin for energy or weight loss is off-label. FDA has not reviewed whether it is safe and effective for that purpose. We did not find an FDA-approved methylcobalamin drug product for any use, including energy, weight loss or 'lipotropic' programs (checked September 27, 2026).

Slowing aging and heart disease

In searches of PubMed, Europe PMC and ClinicalTrials.gov on October 1, 2026, we found no trial of B12 injections, or of B12 given on its own, in adults without a serious illness that measured lifespan, death from any cause, biological age or an epigenetic clock. Among the trials in adults that we found, the ones that counted deaths or measured DNA markers of aging either gave B12 together with folic acid or other B vitamins, or studied people with a serious disease.

The cyanocobalamin products whose labels we reviewed, an injection and a nasal spray, are FDA-approved only for vitamin B12 deficiency and related conditions listed on those labels, not for anti-aging or longevity. Using cyanocobalamin for anti-aging or longevity is off-label. FDA has not reviewed whether it is safe and effective for that purpose. We did not find an FDA-approved methylcobalamin drug product for any use, including anti-aging or longevity (checked September 27, 2026).

A 2018 randomized trial in Germany gave 63 adults with an average age of 68 vitamin D and calcium for 1 year, with or without folic acid, vitamin B6 and 0.5 mg of B12. At 1 year, the group that also got the B vitamins was more likely to have a DNA-based "biological age" above their actual age (odds ratio 5.26, 95% confidence interval 1.51 to 18.28), and the authors described the effect as small. The summary we read does not name the funder.[11] A 2018 analysis of stored DNA data from 44 older adults who had taken a daily tablet of folic acid plus B12 for 2 years in the B-PROOF trial reported a lower epigenetic clock age after the vitamins only in women with one version of the MTHFR gene. The summary we read does not say whether that result was compared with the placebo group. Europe PMC lists UK Medical Research Council grants for the analysis.[12][21]

In a 2007 randomized trial at 36 US Department of Veterans Affairs medical centers, 2,056 adults with advanced kidney disease or kidney failure and high homocysteine took a daily capsule of folic acid, vitamin B6 and 2 mg of B12 or a placebo and were followed for a median of 3.2 years. Death from any cause was the main outcome, and the difference was not significant: 448 people died in the vitamin group and 436 in the placebo group (hazard ratio 1.04, 95% confidence interval 0.91 to 1.18). PubMed lists US government research support for the trial.[8] In a 2010 randomized trial at 33 dialysis centers in Germany, 650 people with kidney failure on hemodialysis got folic acid, B12 and vitamin B6 three times a week after dialysis for an average of 2 years, at either a higher dose (50 micrograms of B12) or a much lower one (4 micrograms of B12). Death from any cause was the main outcome: 102 people (31%) died in the higher-dose group and 92 (28%) in the lower-dose group (hazard ratio 1.13, 95% confidence interval 0.85 to 1.50). PubMed lists research support from outside the US government for the trial, and the summary we read does not name the funder or say how the vitamins were given.[10] A 2009 combined analysis of two randomized trials in Norway followed 6,837 people with ischemic heart disease who took folic acid plus B12 by mouth, with or without vitamin B6, or took vitamin B6 alone or placebo, for a median of 39 months, and were then followed for a further 38 months. Death from any cause was recorded in 16.1% of those given folic acid plus B12 and 13.8% of those not given it (hazard ratio 1.18, 95% confidence interval 1.04 to 1.33). The authors wrote that their results were mainly driven by more lung cancers in the people given folic acid plus B12, and the trials took place in Norway, where foods are not fortified with folic acid. The trials gave B12 only together with folic acid by mouth, so they cannot show what B12 does on its own, and they did not test B12 injections or people without heart disease. We grade this an emerging safety signal. It comes from people with heart disease taking folic acid plus B12 by mouth, and the trials do not show whether it applies to anyone else. PubMed lists research support from outside the US government, and the summary we read does not name the funder.[9] NIH's Office of Dietary Supplements describes a meta-analysis of 18 randomized trials in 74,498 people that found oral products containing B vitamins, including B12, had little or no effect on cancer, cancer deaths or death from any cause over 2 to 7.3 years.[5] None of these trials tested B12 on its own in people without a serious disease, and none shows that B12 slows aging or lengthens life.

In the SEARCH trial of 12,064 heart-attack survivors in the UK, daily folic acid plus B12 tablets for about 6.7 years lowered homocysteine by 28% but did not reduce major heart and blood vessel events, which occurred in 25.5% of the vitamin group and 24.8% of the placebo group.[22] NIH's Office of Dietary Supplements says the available evidence suggests that oral B12, alone or with other B vitamins, does not reduce the risk of cardiovascular disease or of death from it.[5] Lower homocysteine and higher blood B12 are measurements, and changes in them do not show that B12 slows aging or prevents heart disease.

Methylcobalamin instead of cyanocobalamin

In searches of PubMed and Europe PMC on October 1, 2026, we found no randomized trial that compared methylcobalamin with cyanocobalamin or hydroxocobalamin given the same way in people with B12 deficiency. In those searches, the two randomized trials we found that used methylcobalamin for low B12 compared methylcobalamin taken by mouth or under the tongue with hydroxocobalamin injections, so they cannot separate the form of B12 from the way it was given.[14][13] In a 2016 randomized trial of 34 adults with type 2 diabetes who were taking metformin and had low B12, methylcobalamin under the tongue gave a higher blood B12 level at 3 months than a single hydroxocobalamin injection (372.1 against 251.7 pmol/L), and the difference was no longer significant at 6 months.[13] A 1996 preliminary study randomly assigned 20 healthy adults to cyanocobalamin or methylcobalamin and measured sleep and alertness, not B12 deficiency. Sleep time fell in the methylcobalamin group, and the authors concluded that only methylcobalamin had an alerting effect. The summary we read describes no placebo group and does not say how the vitamin was given or who paid for the study.[15] NIH's Office of Dietary Supplements says, "No evidence indicates that absorption rates of vitamin B12 in supplements vary by form of the vitamin." According to NIH's Office of Dietary Supplements, methylcobalamin and 5-deoxyadenosylcobalamin are the active forms of B12 in the body, and cyanocobalamin and hydroxocobalamin become active after the body converts them into those forms. A 2015 review of how the different forms of B12 are handled in the body concluded that methylcobalamin is unlikely to be advantageous compared with cyanocobalamin; the review was about mechanisms, not trial results.[23]

Limitations

In the OB12 trial, blood B12 returning to normal was the main outcome, and symptoms and quality of life were secondary outcomes. The summaries of two older trials name no main outcome and report nerve findings in small groups. The individual trials on this page that compared B12 tablets with injections (OB12, the 1998 and 2003 trials, the gastric bypass trial and the 4-week primary care trial) each followed people for 1 year or less, so they say little about long-term health. Several of the trials on this page tested B12 tablets or combinations of B vitamins rather than B12 injections alone. The UK's NICE guideline advises caution when reading B12 test results in people already using B12 products, including tablets, injections or skin patches, because these may raise blood B12 levels without fully treating a deficiency.[4] This page does not cover B12 injections in children or during pregnancy, and it does not cover B12 for nerve pain.

Risks and side effects

The cyanocobalamin injection labels warn about serious allergic reactions, low potassium when severe anemia is treated, and optic nerve damage in people with early Leber's disease. The cyanocobalamin injection labels warn that anaphylactic shock and death have been reported after B12 injections, and recommend a small test dose into the skin before injecting people suspected of being sensitive to B12. The two cyanocobalamin injection labels we read list serious allergic reactions and low potassium without saying how often they occur, and we did not search for studies that measured how often they happen. The cyanocobalamin injection labels warn that low potassium and sudden death may occur when severe megaloblastic anemia is treated intensively, and say potassium should be checked closely during the first 48 hours of treatment for pernicious anemia.

The cyanocobalamin injection labels report that people with early Leber's disease, an inherited optic nerve disease, who were treated with cyanocobalamin had severe and rapid optic nerve damage. The cyanocobalamin injection labels warn that B12 deficiency left to progress for more than 3 months may cause permanent damage to the spinal cord. The labels also warn that folic acid can improve the blood picture of B12 deficiency without preventing its nerve damage.

Other reactions listed in one cyanocobalamin injection label include fluid in the lungs and heart failure early in treatment, blood clots in the arms or legs, polycythemia vera, mild temporary diarrhea, itching, a short-lived rash and a feeling of swelling of the whole body, and the label gives no frequencies.[2] Some B12 injection vials contain benzyl alcohol, which one label links to a fatal "gasping syndrome" in premature infants, and aluminum, which the label says may reach toxic levels with long-term injections in people with impaired kidney function.[2]

Sources: Cyanocobalamin injection prescribing information, Issued June 2025.

Contraindication considerations

The cyanocobalamin injection labels say that sensitivity to cobalt or to vitamin B12 is a contraindication, meaning a reason not to use the product. Other label cautions that may affect whether B12 injections are suitable include early Leber's disease, premature infants for vials containing benzyl alcohol, and impaired kidney function for vials containing aluminum. Contraindications and cautions differ between B12 injection products, so each product's own label applies.

Sources: Cyanocobalamin injection prescribing information, Issued June 2025.

If you have severe symptoms, call 911 or seek emergency care. Report side effects to FDA MedWatch.

Administration methods

Cyanocobalamin injection, a form of vitamin B12, is given into a muscle or deep under the skin. For pernicious anemia, one cyanocobalamin injection label describes a schedule that starts with 100 micrograms a day for 6 or 7 days, then moves to every other day for seven doses and every 3 to 4 days for 2 to 3 weeks, and then 100 micrograms once a month for life.[2] A licensed clinician sets each person's B12 dose and injection schedule.

Dose schedules on this page summarize the cyanocobalamin injection prescribing information and are not instructions to follow. A prescriber sets and adjusts the dose.

Sources: prescribing information, Dosage and Administration section, for Cyanocobalamin injection prescribing information, Issued June 2025.

The cyanocobalamin injection labels say people with pernicious anemia should be told they will need monthly B12 injections for the rest of their lives. For causes of B12 deficiency that cannot be reversed, the UK's NICE guideline recommends continuing lifelong injections into a muscle, even if symptoms have improved or gone away.[4]

According to the cyanocobalamin injection label, B12 injected into a muscle or under the skin is absorbed quickly and completely, and blood levels peak within 1 hour of an injection into a muscle.[2] The same label says that within 48 hours of an injection of 100 or 1,000 micrograms, 50% to 98% of the dose may appear in the urine, most of it within the first 8 hours.[2]

Are B12 injections FDA-approved?

Cyanocobalamin injection, given into a muscle or under the skin, and cyanocobalamin nasal spray, sprayed into the nose, are FDA-approved prescription products for vitamin B12 deficiency and related conditions listed on the labels we reviewed (checked September 27, 2026).

The FDA status table lists the cyanocobalamin products whose prescribing information we reviewed, with the route and the uses in that prescribing information.

Each cyanocobalamin product in the FDA status table is available only with a prescription (checked September 27, 2026).

Completing an intake form or making a payment does not guarantee a prescription.

Whether a cyanocobalamin product is appropriate for a specific person is decided by a licensed clinician using that product's prescribing information.

We did not find an FDA-approved methylcobalamin drug product for any use (checked September 27, 2026).

Are compounded or "lipotropic" (MIC + B12) shots FDA-approved?

Compounded cyanocobalamin, including blends sold as "MIC + B12" or "lipotropic" shots, is a different product from the cyanocobalamin injection in the FDA status table.

Compounded cyanocobalamin products, including blends sold as 'MIC + B12' or 'lipotropic' shots, are not FDA-approved. FDA states: 'Compounded drugs are not FDA-approved. This means that FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed.' As of FDA's list updated March 21, 2025, cyanocobalamin is on FDA's list of substances under evaluation for use by outsourcing facilities (503B Category 1), and this listing is not an FDA approval of any compounded product.

We did not find an FDA-approved methylcobalamin drug product. FDA's compounding lists (updated May 14, 2026 and March 21, 2025) treat it as a substance that is not part of an approved drug.

Compounded methylcobalamin products, including injections, are not FDA-approved. FDA states: 'Compounded drugs are not FDA-approved. This means that FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed.' As of FDA's lists updated May 14, 2026 and March 21, 2025, methylcobalamin is on FDA's lists of substances under evaluation for use in compounding by pharmacies and by outsourcing facilities, and these listings are not an FDA approval of any compounded product.

Regulatory status checked September 27, 2026. Sources: dailymed.nlm.nih.gov/…/lookup.cfm; dailymed.nlm.nih.gov/…/lookup.cfm; www.fda.gov/…/download; www.fda.gov/…/compounding-and-fda-questions-and-answers; www.accessdata.fda.gov/…/080737Orig1s040lbl.pdf

Regulatory status checked September 27, 2026. Sources: www.fda.gov/…/download; www.fda.gov/…/download; www.fda.gov/…/download; www.fda.gov/…/download; www.fda.gov/…/compounding-and-fda-questions-and-answers

Alternatives: B12 tablets vs injections

In small trials of people with low B12, high-dose B12 tablets raised blood B12 levels about as well as injections over a few months, and most of what these trials reported was blood test results.[24] A 2018 Cochrane review of 3 small trials in 153 people with B12 deficiency found that tablets of 1,000 to 2,000 micrograms a day raised blood B12 levels about as well as injections into a muscle over 3 to 4 months, and it rated the evidence low quality.[24] In the OB12 trial of 283 adults aged 65 and older with low B12 in Madrid, B12 tablets were as good as injections at bringing blood B12 back to normal at 8 weeks, but at 52 weeks 73.6% of the tablet group and 80.4% of the injection group had normal levels, and the tablets were not shown to be as good.[25] In a 4-week trial of 37 adults in primary care (Metaxas 2017), weekly hydroxocobalamin injections raised blood B12 far more than daily cyanocobalamin tablets, although other blood markers of B12 status became normal in everyone in both groups.[26] In a randomized trial of 50 adults with low B12 after gastric bypass surgery (Schijns 2018), methylcobalamin tablets brought blood B12 back to normal as well as hydroxocobalamin injections.[14] Two recent pooled reviews found no statistically significant difference in blood B12 levels between tablets, B12 dissolved under the tongue and injections, but both included non-randomized studies and found large differences between the studies they combined.[27][28]

The Cochrane review says none of its three trials reported on symptoms of B12 deficiency, quality of life or how acceptable people found the treatment, although the published summaries of two of those trials describe nerve problems improving with both tablets and injections.[24][29][30] In a 1998 randomized trial that analyzed 33 people with B12 deficiency, blood and nerve abnormalities were corrected promptly and to the same degree with 2 mg of cyanocobalamin by mouth each day and with 1 mg injections.[29] A 2003 open-label randomized trial in Turkey was completed by 60 people with anemia from B12 deficiency, 26 taking B12 by mouth and 34 getting injections. Its summary reports that nerve problems had improved by day 30 in 7 of 9 people in the tablet group and 9 of 12 in the injection group, and does not say how those 9 and 12 were chosen.[30] In the OB12 trial, quality of life was comparable in the tablet and injection groups, and the trial's full report found no significant difference between the groups in signs of B12 deficiency at any follow-up visit. The trial was funded by the Spanish health ministry through a call for independent clinical research.[25] The 1998 and 2003 trials were small, and we have read only their published summaries, so these results do not show whether tablets and injections are equally good for nerve recovery. In the reports and summaries we read, the tablet-versus-injection trials did not give separate results for people with pernicious anemia, so they do not show that tablets work for pernicious anemia. In the OB12 trial, adverse events were reported by 3.6% of people taking tablets and 4.2% of people getting injections.

One cyanocobalamin injection label says a diet with no animal products, including milk products and eggs, supplies no B12, and that people following such a diet should take oral B12 regularly.[2]

This table shows blood B12 results only. The OB12 trial and two of the three trials in the Cochrane review also reported quality of life, signs of deficiency or nerve findings. In the reports and summaries we read, the tablet-versus-injection trials did not give separate results for people with pernicious anemia, so they do not show that tablets work for pernicious anemia.

Provider directory

Both links below open the Injectable nutrients category of the provider directory.

Compounded cyanocobalamin is not FDA-approved. See FDA's statement.

Compounded methylcobalamin is not FDA-approved. See FDA's statement.

We did not find an FDA-approved methylcobalamin drug product for any use (checked September 27, 2026).

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A licensed clinician decides whether treatment is appropriate. Treatment is not guaranteed.