Vitamin B12 shots are injections that a doctor may prescribe to treat a vitamin B12 deficiency, especially if a person’s body has difficulty absorbing the vitamin.

A deficiency in vitamin B12 can lead to various health problems, ranging from fatigue to permanent neurological changes.

If a person has low vitamin B12 levels due to a health condition, a doctor may recommend oral supplementation or injections of the vitamin.

Injections are usually for people with bodies that have problems absorbing vitamin B12 and those who have undergone gastric surgery. This is because shots enable the body to absorb vitamin B12 without it having to go through the digestive system.

This article addresses the importance of maintaining adequate vitamin B12 levels and outlines the benefits and risks associated with vitamin B12 shots.

Share on Pinterest
Imagesines/Getty Images

Vitamin B12 is an essential water-soluble vitamin that plays a role in many bodily functions, including:

  • DNA production
  • red blood cells
  • nerve cells

Without vitamin B12, a person may start to feel tired and weak due to megaloblastic anemia.

Vitamin B12 is present in many dietary sources, such as:

  • meat
  • fish
  • eggs
  • dairy products
  • nutritional yeast
  • some fortified foods

In animal-based foods, vitamin B12 binds to the protein molecules. During digestion, stomach acid causes it to separate from the protein, and a substance called intrinsic factor enables the bloodstream to absorb it.

Some people’s bodies do not produce enough stomach acid or intrinsic factor if they have a condition known as autoimmune atrophic gastritis. These people may need vitamin B12 shots to reduce their risk of deficiency, which can lead to pernicious anemia.

Other people who may needs shots include those who have had gastrointestinal surgery if their digestive system cannot absorb vitamin B12 efficiently.

The table below contains the recommended dietary allowances (RDAs) for vitamin B12. The RDA refers to the minimum daily amount that most healthy people belonging to a specific group need.

GroupAmount
0–6 months0.4 micrograms (mcg)
7–12 months0.5 mcg
1–3 years0.9 mcg
4–8 years1.2 mcg
9–13 years1.8 mcg
14+ years2.4 mcg
Pregnant people2.6 mcg
People who breastfeed2.8 mcg

However, a doctor can advise on an individual’s specific needs.

Vitamin B12 shots are a form of supplementation that contains a synthetic version of vitamin B12, or cyanocobalamin.

A doctor will inject the shot into the muscle. If they inject it into a vein, the body may lose a high proportion as the person passes urine.

Cyanocobalamin is available in liquid, tablet, and capsule form. Certain foods, such as cereals, may be fortified with the synthetic form of vitamin B12.

Vitamin B12 shots are only available by prescription following a clinical diagnosis of low levels. However, low levels are rare in most healthy adults because the human liver stores vitamin B12 over time.

That said, some people have a higher risk of deficiency and may benefit from vitamin B12 shots or tablets.

People with symptoms of vitamin B12 deficiency

Anyone who has signs and symptoms of a vitamin B12 deficiency or pernicious anemia should consult a doctor.

Signs and symptoms include:

  • difficulty thinking and remembering
  • fatigue
  • heart palpitations
  • pale skin
  • weight loss
  • infertility
  • numbness and tingling in the hands and feet
  • dementia
  • mood changes
  • a sore tongue
  • low appetite
  • constipation

Vitamin B12 deficiency risk factors

The following risk factors can increase the chance of developing vitamin B12 deficiency:

  • high alcohol consumption
  • older age
  • pernicious anemia
  • atrophic gastritis, which refers to inflammation in the stomach
  • Helicobacter pylori infection
  • celiac disease
  • Crohn’s disease
  • a history of gastrointestinal surgery
  • following a plant-based diet
  • pancreatic insufficiency
  • AIDS
  • some hereditary conditions that affect vitamin B12 absorption

People with gastrointestinal issues

Conditions that affect the gastrointestinal tract may affect vitamin B12 release or absorption.

These include:

  • pernicious anemia, which can lead to gastric atrophy, or damage to the stomach
  • fish tapeworm infestation
  • bowel or pancreatic cancer
  • folic acid deficiency
  • overgrowth of bacteria in the small intestine
  • celiac disease
  • Crohn’s disease

Individuals who have undergone gastrointestinal surgery, including weight loss surgery, may have fewer of the cells necessary to secrete stomach acid and intrinsic factor. This can also affect vitamin B12 absorption.

Older adults

Research from 2015 suggests that vitamin B12 deficiency is more likely to affect those aged over 60 years and that some people may benefit from vitamin B12 injections.

The scientists found that older adults have a higher risk of conditions linked to reduced stomach acid production, including gastric atrophy. Low stomach acid also enables certain bacteria to grow, and these can use up vitamin B12 stores.

Vegetarians and vegans

Vitamin B12 mainly occurs in animal foods, so people who follow a plant-based diet have a higher risk of vitamin B12 deficiency.

Research from 2010 looked at data from 689 men and found higher rates of vitamin B12 deficiency in those who consumed a plant-based diet. Over half of those who were vegan and 7% of those who were vegetarian had low vitamin B12 levels, compared with under 1% of people who ate meat.

Vegetarian or vegan people who are pregnant may need to take supplements or consume fortified foods, as vitamin B12 transfers to the baby via the placenta and breast milk. If the infant is entirely breastfed, they may not consume enough vitamin B12. This can lead to permanent and severe neurological issues.

In rare cases, a doctor may recommend injections, but research suggests that taking additional vitamin B12 by mouth can be as effective as receiving an injection in a muscle. It is also less costly.

A doctor may recommend vitamin B12 shots for people who are at risk of a deficiency or its complications.

Vitamin B12 shots may help reduce the risk of the following conditions:

  • heart disease
  • stroke
  • neurological disorders
  • problems with thinking and memory
  • vision loss
  • infertility
  • neural tube defects in children born to those with a vitamin B12 deficiency

There is no upper limit for the intake of vitamin B12 because the risk of toxicity or overdose is low. However, vitamin B12 shots may have other side effects.

If a person experiences the following, or if these issues persist or worsen, they should seek medical advice:

  • pain, redness, or itching at the site of the injection
  • mild diarrhea
  • a swelling sensation in the body
  • temporary itching of the skin

There may also be a risk of:

If anyone experiences difficulty breathing, hives, and swelling, they need emergency medical help. They may be experiencing anaphylaxis, which is a severe allergic reaction.

Drug interactions

Vitamin B12 may interact with certain medications. People must always inform a doctor about all prescription and over-the-counter drugs they are taking before receiving a vitamin B12 shot.

Some commonly prescribed medications that may interact with vitamin B12 include:

Allergies and medical conditions

Those who have allergies or medical conditions should always inform a doctor before receiving a vitamin B12 shot.

Vitamin B12 shots may not be suitable for people with a history of:

  • sensitivity to vitamin B12
  • Leber’s disease, which affects the optic nerve
  • kidney problems
  • hypokalemia, or low potassium levels
  • deficiencies in other nutrients, particularly folic acid and iron

Most people get enough vitamin B12 from their diet, but some people have a deficiency. This can be due to having low levels of intrinsic factor in the digestive system, having a digestive condition, or following a plant-based diet.

The 2020–2025 Dietary Guidelines for Americans recommend meeting the need for vitamin B12 and other nutrients through diet first and foremost.

If dietary sources are insufficient, however, a doctor may recommend supplementation through pills or injections, depending on the cause of the deficiency.