Vitamin B12 shots are injections that a doctor may prescribe to treat a vitamin B12 deficiency. They may be useful for those with gastrointestinal issues, older adults, vegans, and vegetarians.

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

Vitamin B12 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 going 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.

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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 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

Discover some of the best B12-containing foods here.

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.

How long do vitamin B12 shots last?

How often a person will require shots depends on what is causing their B12 deficiency. Initially, a person may need B12 supplementation shots every day for around two weeks or until symptoms improve.

If the cause of a person’s B12 deficiency is their diet, they may not require further shots or only require them once or twice per year.

In cases where a chronic condition is causing a deficiency, people may require B12 shots around every 2 months.

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.

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 needing shots include those who have had gastrointestinal surgery if their digestive system cannot absorb vitamin B12 efficiently.

People with symptoms of vitamin B12 deficiency

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

Signs and symptoms include:

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:

Individuals who have undergone gastrointestinal surgery, including weight loss, may have fewer 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 over 60 years and that some people may benefit from vitamin B12 injections.

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.

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.

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 chestfed, they may not consume enough vitamin B12. This can lead to permanent and severe neurological issues.

Discover the best vegan and vegetarian sources of B12 here.

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

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 chestfeed2.8 mcg

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

A doctor may recommend vitamin B12 shots for people 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.

After having a B12 shot, a person should monitor for adverse symptoms and seek medical help if they experience:

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

In rare cases, a person may also be at 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.

Medications side effects

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

Some other prescription medications can directly cause a vitamin B12 deficiency. These include:

Allergies and medical conditions

Those with 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

Here are some frequently asked questions about vitamin B12 injections.

What does a B12 shot do for you?

Vitamin B12 injections provide the individual with a synthetic version of vitamin B12. A doctor may recommend vitamin B12 shots if a person has a vitamin B12 deficiency.

Do vitamin B12 injections work immediately?

Vitamin B12 injections typically begin to work straight away. However, it may take a number of days or weeks before a person notices improvements in their symptoms.

What should you not do after a B12 shot?

Precautions a person may need to take after receiving a B12 injection may depend on which side effects they experience. For example, if they experience dizziness, they should avoid driving. A person’s doctor can provide them with information about any specific activities they may need to avoid or any other considerations. This might include limiting alcohol intake.

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.

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