Potential Vitamin B12 Injection Side Effects

Updated August 16, 2022
man getting Vitamin B12 injection

Vitamin B12, or cobalamin, is a natural vitamin found in animal foods like dairy and meat. B12 is responsible for several processes within the body, like red blood cell formation and the production of DNA.

People with a B12 deficiency might seek out a vitamin B12 injection. Side effects can occur, however. In general, vitamin B12 supplements are not considered harmful. But it can be helpful to learn about potential risks to decide if getting a vitamin B12 injection is right for you.

Common B12 Injection Side Effects

Physicians may prescribe vitamin B12 injections, also known as cobalamin or cyanocobalamin injections, to patients suffering from vitamin B12 anemia, fatigue, or other symptoms of vitamin B12 deficiency. According to StatPearls, patients with pernicious anemia require lifelong vitamin B12 injections and may want to consider dietary changes for B12 deficiency. These injections can be painful, as the vitamin is injected under the skin (subcutaneously) or into a muscle (intramuscularly).

According to StatPearls, vitamin B12 injections are generally considered safe as long as they are administered properly. However, there are side effects patients may experience from the injections. Common side effects reported by the Mayo Clinic include:

  • Diarrhea
  • Headache
  • Nausea

If these side effects become severe or troublesome, let your healthcare provider know immediately.

More Serious B12 Injection Side Effects

Although rare, vitamin B12 injections can cause some severe side effects. The injections can create problems in various body parts like the heart, lungs, skin, brain, and muscles. MedLine Plus and other sources report that some of the side effects may be severe. If you experience these side effects, contact your healthcare provider immediately.

Cardiovascular and Respiratory Effects

The cardiovascular system includes your heart and blood vessels. The cardiovascular system closely connects to the respiratory system and oxygenates your lungs. Adverse reactions after a B12 injection may include:

  • A feeling of tightness in the chest
  • Anaphylaxis (difficulty breathing or swallowing)
  • Chest pain
  • Congestive heart failure
  • Heart palpitations
  • Pulmonary edema
  • Rapid heartbeat (tachycardia)
  • Shortness of breath
  • Vascular thrombosis

Musculoskeletal Effects

woman with leg pain from Vitamin B12 injection

Your musculoskeletal system makes up your bones, tendons, cartilage, and connective tissues. Vitamin B12 injections can cause issues with:

  • Leg pain
  • Muscle pain
  • Muscle weakness
  • Swelling in arms and lower extremities
  • Swelling or pain in one leg
  • Unstable walking

Neurological Effects

The neurological effects of vitamin B12 affect your brain. You may experience severe side effects like:

  • Confusion
  • Dizziness
  • Extreme tiredness

Dermatological Effects

Most skin reactions from a B12 injection come from an allergic reaction. Just a few skin reactions you might notice include:

  • Hives
  • Itching
  • Red, swollen, blistered, or peeling skin with or without fever
  • Skin rash

Inform your healthcare provider immediately if you experience anything unusual while taking B12 injections.

Possible B12 Injection Contraindications

There are several potential contraindications or reasons not to receive treatment with B12 injections. Before starting vitamin B12 injections, tell your healthcare provider if you are pregnant or lactating.

In addition, speak to your healthcare provider about any medications that you are taking. You should also check with the provider that has prescribed the vitamin B12 injections before adding any new medication. St. Luke's Hospital lists the following drugs as those that might possibly interact with B12 injections.

Lastly, it is also essential that you communicate with your provider if you have kidney disease or an allergy to cobalt or any other medication, vitamin, dye, food, or preservative.

Although severe allergic reactions are very rare, they have occurred. This type of allergic reaction can be life-threatening. Medical professionals and researchers are not clear if the allergic reaction is caused by the preservatives or other substances found in the injection solution or the vitamin itself. Hives, wheezing, and difficulty breathing are all signs of severe allergic reactions that require immediate medical attention.

Was this page useful?
Potential Vitamin B12 Injection Side Effects