Everything To Know About Vitamin B12 Injections

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The body needs a large range of vitamins and minerals in order to function properly. When we become deficient of these vitamins, we can suffer from malnutrition. Malnutrition is associated with many adverse health effects – but it is important to note that each vitamin plays a different role in the human body. Thus, being sufficient of a certain vitamin is prone to cause very specific symptoms and side-effects to develop.

Vitamin B12 is a crucial nutrient that plays a role in the production of energy within the human body. The vitamin is also responsible for assisting with the process of producing proteins. There are many other important roles that vitamin B12 plays in the body. Failure to obtain enough of this vitamin can lead to serious complications.

When a person is deficient of vitamin B12, a physician may recommend the use of a vitamin B12 injection. These injections contain a synthetic form of the vitamin, known as Cyanocobalamin, and can help to restore optimal levels of vitamin B12.

In this article, we analyze the pros and cons of a vitamin B12 injection, consider the roles of this vitamin, and we look at some of the most important signs of a vitamin B12 deficiency.

What Is Vitamin B12 And What Functions Does This Nutrient Have In The Human Body?

Vitamin B12 forms part of the B vitamin family. The body does not make this vitamin itself, but rather requires it from food sources. The vitamin is known to be an enzyme cofactor. Specifically, vitamin B12 acts as a cofactor for two different types of enzymes in human body1.

This vitamin is water-soluble, which means there is no need to be concerned about taking it with fat content. It is present in a relatively small number of foods, but can also be taken through a daily dietary supplement. There are also prescription versions of vitamin B12 available, but these are usually only provided to a person when they have a deficiency of this particular nutrient.

There are different forms of vitamin B12, each with their own specific function in the human body. Cobalt, a type of mineral, is contained within this vitamin. Cobalamins is a term used to refer to the compounds that possess the activity of vitamin B12.

The two primary forms of vitamin B12 that are involved in the metabolism of the human body include2:

The vitamin has a relatively large number of functions to play in the human body, including:

  • The synthesis of DNA
  • Neurological functionality
  • The formation of red blood cells

There is also an indirect relation that vitamin B12 plays with lipids, proteins, hormones, and the DNA of the human body. Methionine, a type of enzyme, needs vitamin B12 to function properly.

How Much Vitamin B12 Do You Need?

The specific amount of vitamin B12 that is needed for optimal bodily function depends on a couple of factors. The gender of a person will have an impact, along with age. The specific reason why a person will be taking vitamin B12 also affects how much of the supplement is needed. When simply using vitamin B12 to maintain proper levels, a lower dose would be needed compared to providing a person that is suffering from a deficiency of this nutrient with a supplement.

The general dosage recommendation for a person who is aged 15 years or older is usually about 2.4 mcg of vitamin B12 on a daily basis. The source of the vitamin will affect how much to take, however. For example, when taking a supplement that contains vitamin B12, very little of the compound will actually be absorbed into the body.

Signs Of A Vitamin B12 Deficiency

Before considering vitamin B12 injections or taking a higher amount of these supplements, it is important to note that there are certain signs that may signal a deficiency of this nutrient. When these signs are not present, it is generally not advised to take more than what is recommended. Furthermore, a doctor can also conduct blood tests to determine if a person may have an actual deficiency of vitamin B12.

Below, we share some of the most important signs that a vitamin B12 deficiency may be present3:

  • Weakness
  • Lightheadedness
  • Tiredness
  • Pale skin
  • Heart palpitations
  • Shortness of breath
  • Tongue that has a texture that is smoother than usual
  • Constipation
  • Loss of appetite
  • Gas
  • Diarrhea
  • Nerve problems
  • Vision problems
  • Muscle weakness
  • Behavioral changes
  • Memory loss
  • Depression

Possible Complications Of A Vitamin B12 Deficiency

Recognizing a deficiency in vitamin B12 is very important. When this type of deficiency develops, and it is not addressed, then there is a large number of complications that may develop. This is because of the important role that vitamin B12 plays with the production of red blood cells, nerve health, and other functions of the human body.

Vitamin B12 deficiency anemia is one of the most important complications that we need to address here. When the anemia becomes severe, tachycardia may develop. In some cases, heart failure is another risk that should be taken into consideration.

Vitamin B12 deficiency anemia has also been linked to complications such as4:

All of these can be exceptionally unpleasant. When symptoms associated with vitamin B12 deficiency develops, taking action before these complications develop can help to reduce the risks and damage dealt with the body.

How Does Vitamin B12 Injections Work?

Vitamin B12 injection is a pharmaceutical product that can be provided to a patient upon a prescription by a physician or specialist. A vitamin B12 injection utilizes an ingredient known as Cyanocobalamin. This is a synthetic type of chemical that is man-made. The chemical structure of Cyanocobalamin is similar to that of vitamin B12, which means it can produce similar effects in the patient’s body as vitamin B12.

While vitamin B12 injections do need to be provided with a prescription, it is important to note that, in some cases, the injections may be administered at home. Full instructions are given to the patient when they are prescribed with this medication, ensuring the individual is able to administer the injection without suffering potential risks.

In some cases, the injection needs to be administered directly into a muscle in the patient’s body. There are other times where the injection will rather be administered underneath the skin of the patient. It is important that this is discussed with a physician in order to determine what the best method of administration would be for a particular person.

Generally, taking an injection that contains Cyanocobalamin is considered a more ideal option compared to using a dietary supplement that is taken orally. This is because the substance is injected directly into a muscle and includes a type of vitamin B12 that is already in its free form, allowing the body to use the nutrient more effectively. Furthermore, it is also possible to achieve greater control in terms of the dosage when using a Cyanocobalamin injection.

Vitamin B12 Injection Dosage

The dosage that will be used when a vitamin B12 injection is provided to a person depends on factors like age and gender, similar to taking a standard supplement. This, however, is a more targeted way of dealing with a vitamin B12 deficiency, and there are other factors that need to be taken into account.

For an appropriate dosage to be identified, a person would first need to have blood tests done. The blood tests will determine how much vitamin B12 is currently in a person’s body. This will help a physician determine how severe the deficiency is. If a specific complication or condition has developed due to the presence of such a deficiency, then this is something that needs to be accounted for as well. The physician will take all of these factors into account when deciding how much vitamin B12 should be administered to the patient in the form of a Cyanocobalamin injection.

Can A Vitamin B12 Injection Cause Side-Effects?

Due to the fact that this medication is administered through an injection to the patient, it is important to consider whether side-effects may develop. As with any other type of injection, there is a risk of itchiness and pain at the side of the injection. Redness may also develop for a few hours following the injection.

Some patients may experience side-effects to the actual content that is injected into their bodies. In the majority of cases, these side-effects will be temporary and will not cause alarm. The most common side-effects that the patient may experience include:

  • Mild diarrhea
  • A swollen sensation throughout the body

Low potassium is a possible complication that some patients can experience when they obtain a vitamin B12 injection. This condition is called hypokalemia. Common symptoms of low potassium in the blood circulatory system may include:

  • Irregular heartbeat
  • Weakness
  • Muscle cramps

When these symptoms develop following the administration of a vitamin B12 injection, the person should report this to their physician.

Allergic reactions to the Cyanocobalamin in these injections are extremely rare. Still, this is something that can occur in a small number of people who receive one of these injections. Symptoms of such an allergic reaction may include:

  • Swollen throat
  • Swollen tongue
  • Swelling of the face
  • Severe dizziness
  • Rash
  • Itchiness
  • Trouble breathing

These symptoms need to be reported to a physician immediately. It would also be a good idea to seek urgent medical assistance with the allergic reaction as well.

Precautions That Need To Be Noted

There is a couple of precautions that people should be aware of before they have a vitamin B12 injection. The most important precautions that we need to note here is the fact that the individual need to advise the prescribing physician of specific conditions that they might have, including:

  • Leber’s disease
  • Folic acid deficiency
  • Iron deficiency
  • Gout
  • Existing hypokalemia
  • Polycythemia vera
  • Kidney disease

There are also some risks associated with the use of vitamin B12 injections during pregnancy. When a woman is pregnant, vitamin B12 injections only need to be prescribed to a patient when it is absolutely necessary. The physician will discuss the pros and cons of using the medicine with the patient before prescribing the injection.

Possible Interactions

There is a couple of things to note when it comes to looking at interactions and vitamin B12 injections.

In particular, certain types of drugs are known to cause interference with ensuring vitamin B12 levels can be effectively detected during a blood test at a laboratory. These drugs include:

  • Amoxicillin
  • Erythromycin
  • Pyrimethamine
  • Methotrexate

It should also be noted that there are certain drugs that may have an interaction with the Cyanocobalamin that is contained in this particular injection. The drugs that need to be noted here include:

  • Anti-cancer drugs
  • Drugs used to manage HIV
  • Chloramphenicol

Individuals who are using existing nutrition supplements should also be wary. This is especially the case when the person is already taking daily folic acid supplements.


Vitamin B12 injections can assist in restoring optimal levels of this nutrient in the body, which can be useful in cases where a deficiency of the vitamin has developed.

Without optimal treatment, vitamin B12 deficiency can lead to harmful complications.

Patients need to ensure they are thoroughly educated about the symptoms that a vitamin B12 deficiency may cause. While the presence of these symptoms does not necessarily mean a vitamin B12 deficiency is present, but this is still a possibility that should be considered.


1 L.H. Allen. Vitamin B-12. Advanced in Nutrition: An International Review Journal. 5 Jan 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3262614/

2 Vitamin B12 – Fact Sheet For Health Professionals. National Institutes of Health: Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

3 Vitamin B12: What to Know. WebMD. https://www.webmd.com/diet/vitamin-b12-deficiency-symptoms-causes#2

4 Vitamin B12 or folate deficiency anaemia: Complications. NHS. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/complications/

1 Comment
  1. Reply
    david a minshall September 28, 2020 at 9:32 pm

    I am extremely allergic to diagnostic dyes containing iodine. Cardiac arrest etc. When receiving a B-12 shot I quickly developed softball sized hives that lasted about 2 weeks. I had to go to the ER twice. Is there iodine in the B-12 shot or was it something else? I am also allergic to all forms of penicillin and ibuprofen.

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