Vitamin B12 Injections: When Clinicians Use Them, What the Evidence Shows and Wellness-Clinic Claims
Why clinicians give vitamin B12 injections, what trials found when oral B12 was compared with injections, and what is known about wellness-clinic shots for energy.
Content last updated . This page has not been medically reviewed.
Urgent first: allergic reactions
Serious allergic reactions to hydroxocobalamin injections are rare, but the NHS lists symptoms such as a swollen throat or tongue, a raised itchy rash or difficulty breathing. [1] If this happens after any injection, seek emergency medical help right away (911 in the US). This page is information only. If you think you may be short of vitamin B12, see a clinician rather than treating yourself: the NHS notes that some problems from untreated deficiency can be irreversible. [2]Why clinicians give B12 injections
Injections are a medical treatment for some people. For vitamin B12 deficiency anaemia, the NHS says treatment is usually injections of vitamin B12, called hydroxocobalamin, given by a GP or nurse. [3] The most common cause of B12 deficiency in the UK is pernicious anaemia, which is not related to diet. [3] See pernicious anemia and intrinsic factor for why the vitamin is not absorbed in that condition.The NHS describes the length of treatment as depending on the cause. When deficiency is not caused by a lack of B12 in the diet, it says people will usually need an injection every 2 to 3 months for the rest of their life. [3] Those details are UK practice. The schedule, the form of B12 used and the country's rules can differ, so follow your own clinician's plan.
MedlinePlus (US) says a prescription form of vitamin B12 can be given by injection or as a nasal gel. [4]
What trials compared injections with tablets
Evidence label: established nutritional role / deficiency treatment for people with confirmed deficiency; see the table for how strong each finding is.| Question | What the source found | Strength of evidence |
|---|---|---|
| Oral vs injected B12 in people with deficiency | A 2018 Cochrane review found only three randomised trials with 153 participants. [5] It concluded that oral and injected B12 had similar effects on normalising blood B12 levels, with oral treatment costing less. [5] | Low quality |
| Symptoms and quality of life | No trial in that review reported clinical signs and symptoms, quality of life or acceptability. [5] | Proper evidence not found in those trials |
| Oral vs injected in confirmed deficiency (earlier assessment) | A 2013 Ontario analysis rated the evidence as moderate that oral supplements are as effective as injections. [6] | Moderate |
| Oral treatment with severe nerve symptoms | A 2020 review of oral and nasal B12 in older adults says the effect of oral treatment with severe neurological manifestations has not yet been adequately documented. [7] | Insufficient evidence |
Biomarker change (a blood B12 level) is not the same as feeling better. Those trials studied people who were deficient, so their results do not transfer to people with normal B12. The NHS says some people take tablets and others need injections depending on the cause. [3]
Shots at wellness clinics for energy
Clinic menus sometimes offer B12 shots for energy or "boosting" without any test. Proper evidence not found for this use in people who are not deficient: we searched PubMed (2026-10-23) for randomised trials of B12 injections for energy or fatigue and found none we could read for general fatigue.One placebo-controlled crossover trial gave 1000 mcg cyanocobalamin injections to 20 singers who had mild voice symptoms and no known or suspected B12 deficiency. [8] Those singers rated their voice no differently after B12 than after salt-water placebo. [8] That is a small trial on one outcome, so it cannot settle other claims, but it shows why a good feeling after a shot does not prove the vitamin caused it. For the broader claim, see vitamin B12 and energy and IV vitamin therapy claims.
Related pages
Start with vitamin B12 deficiency, B12 tests and the main vitamin B12 profile. Talk to a clinician or pharmacist before starting or stopping any B12 treatment.Frequently asked questions
Do I need a B12 injection?
Only a clinician can say. Injections are used for people with confirmed deficiency, especially when the vitamin is not absorbed well. [3] Tablets work for some causes. [3]
Do B12 shots give you energy?
Proper evidence not found for people who are not deficient. In one placebo-controlled trial of singers without deficiency, injections did no better than placebo on voice measures. [8] See a clinician if tiredness persists, because the NHS lists extreme tiredness among many possible effects of deficiency and says it is diagnosed with symptoms and a blood test. [2]
Are B12 tablets as good as injections?
In people with deficiency, a Cochrane review found low-quality evidence of similar blood B12 levels. [5] Whether tablets are right depends on the cause, which a clinician decides. [3]
What are the side effects of a B12 injection?
Common ones listed by the NHS include pain, swelling or itchy skin where the injection was given. [1] Rarely, a serious allergic reaction can happen. [1]
Can I have a B12 injection during pregnancy?
The NHS says you can usually have hydroxocobalamin injections when pregnant, but to check with a pharmacist or doctor first. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Side effects and cautions
- Medicines and supplements: tell the prescriber about all medicines, herbal remedies, vitamins and supplements. [1] See medication interactions.
- Pregnancy and breastfeeding: the NHS says injections can usually be given in pregnancy, but to check with a pharmacist or doctor first. [1]
- Folic acid: the NHS says folic acid treatment can improve symptoms so much that it hides an underlying B12 deficiency, and that a GP checks B12 levels before folic acid treatment starts. [3]
- Kidney or liver conditions and surgery: ask the treating clinician. We found no source we could read that gives guidance for these on this page.
- Quality: products sold outside clinical care vary. See quality testing and certifications.
References
- NHS (UK), Hydroxocobalamin: medicine information. Read 2026-10-23.
- NHS (UK), Vitamin B12 or folate deficiency anaemia. Read 2026-10-23.
- NHS (UK), Vitamin B12 or folate deficiency anaemia: treatment. Read 2026-10-23.
- MedlinePlus (US National Library of Medicine), Vitamin B12, review date January 2025; reference intakes there are the US Dietary Reference Intakes. Read 2026-10-23.
- Wang H, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database of Systematic Reviews, 2018. Read 2026-10-23.
- Health Quality Ontario, Vitamin B12 and cognitive function: an evidence-based analysis. Ontario Health Technology Assessment Series, 2013. Read 2026-10-23.
- State of the art review: oral and nasal vitamin B12 therapy in the elderly. QJM, 2020. Read 2026-10-23.
- Effect of vitamin B12 injection on the vocal performance of professional singers: a randomized, double-blind, placebo-controlled, crossover trial. JAMA Otolaryngology-Head & Neck Surgery, 2021. Read 2026-10-23.