List of Vitamin B12 Injections Side Effects


Many people seek vitamin B12 injections. While the injections are generally considered safe, in some cases side effects may occur.

Common Side Effects

According to The Mayo Clinic, vitamin B12 injections are generally recognized as safe as long as they are administered properly. However, there are many side effects patients may experience from injections of vitamin B12. UptoDate, a physician-authored clinical decision support resource, indicates common side effects include:

  • Mild diarrhea
  • Upset stomach
  • Nausea
  • Sensation of pain and/or warmth at the site of the injection
  • Feeling swollen over the entire body
  • Headaches
  • Joint pain

If any of these side effects become severe or troublesome, let your doctor know right away.

Although no evidence correlates B12 injections and changes in odor, vitamin B12 does have a connection to smell. Some individuals report they smell after taking B12 supplements. People claim it is a strange odor affecting their body odor and urine. Although no published scientific literature addresses this side effect, it could be possible, as everyone reacts differently to medications and supplements. If you experience a side effect of this nature, speak with a health care provider immediately.

Serious Side Effects

Although rare, vitamin B12 injections can cause some serious side effects. The injections can create problems in various body parts. According to UptoDate your heart, lungs, muscles, nerves, and skin may be affected.

Cardiovascular Effects

The following heart and lung symptoms may occur:

  • A rapid heartbeat
  • Heart palpitations
  • Chest pain
  • A feeling of tightness in the chest
  • Difficulty breathing

Musculoskeletal Effects

The following are possible musculoskeletal effects:

  • Muscle weakness
  • Muscle pain
  • Muscle cramps
  • Leg pain
  • Swelling of the extremities including hands, arms, lower legs, feet, or ankles

Neurological Effects

Vitamin B12 injections may cause the following neurological side effects:

  • Confusion
  • Numbness
  • Dizziness
  • Balance issues
  • Burning, numbness, or tingling
  • Extreme tiredness or fatigue

Dermatological Effects

You may notice the following dermatological symptoms with B12 injections:

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

Metabolic Effects

The following metabolic side effects may occur:

  • A feeling of extreme thirst
  • Frequent urination
  • Any unexplained bruising or bleeding
  • Rapid weight gain

Other vitamin B12 injections side effects may also occur. If you experience anything unusual while taking B12 injections let your doctor know as soon as possible.

Vitamin B12 Injections

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 the National Institutes of Health, 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).

Possible Contraindications

There are a number of potential contraindications to B12 injections. Before starting vitamin B12 injections make sure to tell your doctor if you are pregnant, lactating, or have any of the following conditions.

  • Kidney disease
  • Liver disease
  • An infection
  • Iron deficiency
  • Folic acid deficiency
  • Receiving any treatment that has an effect on bone marrow
  • Taking any medication that has an effect on bone marrow
  • An allergy to cobalt or any other medication, vitamin, dye, food or preservative

Leber's Disease

Anyone that has or has ever had Leber's disease should not take vitamin B12 injections. Leber's disease, also known as LHON, is hereditary optic neuropathy which causes slow painless vision loss. The vision loss occurs first in one eye and then in the other eye. Vitamin B12 injections can exacerbate this condition.

Severe Allergic Reaction

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 to the vitamin itself.

Hives, wheezing, and difficulty breathing are all signs of serious allergic reaction that require immediate medical attention.

Prescription and Nonprescription Drug Interactions

It is important to let your doctor know all the prescription and over-the-counter medications that you take. You also need to include any herbal products, vitamins, minerals, and nutritional supplements you take on a regular basis. Accurate reporting of all medications and supplements can help you avoid dangerous drug interactions.

The National Institutes of Health Office of Dietary Supplements list the following drugs as those that might possibly interact with B12 injections.

Always check with the doctor that has prescribed the vitamin B12 injections before adding any new medication.

Be Informed

If you receive vitamin B12 injections, serious side effects may occur. Be aware of dangerous drug interactions and know what to watch for; this makes taking vitamin B12 injections that much safer.

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List of Vitamin B12 Injections Side Effects