What are the side effects of vitiam b12 shots?

Updated April 17, 2017

Vitamin B12 injections are used to treat patients who suffer from anaemia, fatigue or any other symptoms related to a deficiency in vitamin B12. The shots are sometimes painful and can also sometimes have side effects. While most side effects for B12 shots are mild, some can be quite serious and even fatal. These are rare occurrences, but patients considering whether to take Vitamin B12 shots should be aware of all side effects to make well-informed decisions about their health.

Common Side Effects

There are different side effects to vitamin B12 injections, but the most common tend to be the most mild. Therefore, injecting vitamin B12 is relatively safe. Some of the more common side effects include mild diarrhoea, mild stomach pains, nausea, some pain or warm sensations in injection area, swelling sensations, headaches and joint pain. There is the possibility that any of these symptoms could become severe. In that case, a doctor should be consulted.

Serious Side Effects

The more uncommon and rare side effects are also the most serious. Therefore if any of these symptoms should surface after B12 shots are injected, then a doctor should be consulted. These side effects include rapid heartbeat or heart palpitations; tightness or pains in the chest or the leg; weight gain; weakness in the muscles or muscle cramps; thirstiness; frequent urination; confusion; numbness or tingling sensations; dizziness; breathing and swallowing difficulties, or shortness of breath after mild activity or while lying prone; coughing or wheezing; fatigue; swelling in the limbs, particularly in one leg, hands, feet, or ankles; reddening of the skin on the face or any area of the body; hives; itching or rashes.

Allergic Reactions

Though rare, allergic reactions to vitamin B12 shots are also possible. Allergic reactions to vitamin B12 shots can become life threatening, therefore it is extremely important to consult a doctor if patient has any allergies that might affect or interfere with shots.

Previous Conditions

A physician should also be consulted about previous conditions that are being treated, as that could lead to adverse side effects with injections of vitamin B12. Some of these previous conditions include Leber’s disease, kidney and liver diseases, infections, iron and folic acid deficiencies, treatments to and medications for bone marrow and any and all allergies to other substances, including cobalt.


Prescription and non-prescripton drugs and medications will also create adverse side effects when taken alongside injection shots of vitamin B12. Alcohol, antibiotics, potassium supplements and vitamin products are a few of the prescription and non-prescription drugs and medications that should not be taken along with vitamin B12 shots.

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