Vitamin B12 injections, also known as cobalamin or cyanocobalamin injections, are administered to patients with deficiency of B12 and symptoms associated with the deficiency, such as fatigue and anemia. B12 injections are given to patients who have low resistance to diseases and remain sick from common illness for long period of time.

Although it is better to consume foods rich in vitamin B12 naturally, such as meat, fish, and dairy products, often the doctor may recommend the supplement of Vitamin B12 in injection form. Injections are beneficial to those individuals who show signs of vitamin B12 deficiency but are unable to absorb it into the body.

Injecting B12 shots are often painful to those sensitive to injections, because they are injected deep into the muscle under the skin.

Common Side Effects

Side effects of vitamin B12 injections vary from person to person depending on the mode of delivery and the health of the person. Some side effects are temporary and may last for just a few days.

Some of the most common side effects are:

1. Muscle cramps:

Some people get cramps or spasms in their muscles after injecting vitamin B12 shots. This will occur usually within 6 hours of receiving the injection.

2. Sleeplessness:

Insomnia, or the inability to sleep, is a commonly-occurring side effect of receiving a vitamin B12 injection.

3. Skin infections and Acne:

Shots of Vitamin B12 may lead to some skin infection, known as Folliculitis, around the hair follicles. Acne may also develop on skin accompanied by skin rashes.

4. Nausea and Headache:

Runny nose and headache are other common side effects after injecting vitamin B12. Some people might experience shortness of breath, unusual coughing, or unusual wheezing.

5. Stomach upset:

Another common side effect of B12 injections is upset stomach followed by diarrhea, difficulty in swallowing food, and feeling of extreme dizziness. A few patients may also feel extreme thirst and tiredness.

6. Rapid heart beat:

Some patients have reported rapid palpitation of the heart and a sensation of heart burn accompanied by chest pain.

Uncommon Side Effects:

There do exist some side effects, though not very common, that may be severe, and possibly life threatening.

1. Clotting of Blood:

Blood clots in the arteries of legs and arms, followed by swelling of the affected areas known as peripheral vascular thrombosis, a serious condition that has the potential to cause loss of limb or even loss of life.

2. Severe Allergic reaction:

Severe allergic reaction is very rare but can be life threatening. Researchers and medical professionals alike question whether the allergy is caused by preservatives in injection or by the vitamin itself. Vitamin B12 injections should be avoided by persons who are allergic to cobalt or cobalamin, as it may lead to allergies.

3. Vision loss in case of “Leber’s Disease”:

A person who has or has had Leber’s Disease should not take vitamin B12 injections, since it can result in optic nerve damage (and possibly blindness). Leber’s Disease is hereditary optic neuropathy which will cause slow vision loss, first in one eye and then in the other eye.

4. Pulmonary Edema:

In very rare cases, fluids get accumulated in the lungs of the person taking vitamin B12 injections, a condition known as pulmonary edema. The person may experience pain in the chest and shortness of breath.

This is not an exhaustive list of side effects. There are others. Please do some research to become informed, and always consult with your doctor if you suspect that you are experiencing side effects to any medication.