Vitamin B12 is to the human body what gasoline is to a car; without it, you're not getting anywhere. A diet that includes meat, fish, and dairy products can provide natural sources of B12; however, these foods typically carry a heavy toxic load. Vegetarians and vegans can suffer from B12 deficiency, so can meat eaters, making B12 deficiency a common concern many people solve with supplementation or a B12 injection.
What is a Vitamin B12 Shot?
The shot delivers a high dose of therapeutic B12, usually in the form of cyanocobalamin or hydroxocobalamin. For those who don't care for a shot, oral supplementation with the two active forms of B12, methylcobalamin and adenosylcobalamin, may be as effective as a B12 shot. 
Those who cannot digest or absorb B12 as a result of inherited genetics or damage to the stomach and small intestine require more than can be absorbed from sublingual supplementation. In situations where a high dose is needed, or where injection is the only option, the B12 shot is used. In some cases, B12 shots are used as an energy booster, since B12 plays a critical role in cellular energy production.
Reasons for a B12 Shot
Vitamin B12 deficiency symptoms include depression and mood disorders, fatigue, memory failure, anemia, low blood pressure, and high homocysteine levels. While the shot addresses B12 deficiency, it may also be prescribed to boost energy, as a therapy for depression, or to drive cognitive function. Researchers are also exploring its potential as a therapy for bipolar disorders, shaky leg syndrome, and autism.
Getting the B12 Shot
Before getting the shot, make sure to inform your doctor of any allergies, nutritional supplements you may be taking, or if you’ve recently consumed large amounts of alcohol. At the appointment, the doctor or healthcare professional delivers the shot directly into muscle, usually into the thigh or upper arm, for easy absorption into the bloodstream.
B-12 Shot Side Effects
The dosage amount and the type of B12 used appears to have some control over side effects. As a note, the common side effects of excess vitamin intake include flushing, diarrhea, nausea, and vomiting. Here are the side effects you might experience from the two common B12 shots:
This form of B12 is the one we find in our food. When delivered as a B12 shot, mild side effects may include soreness at the injection site, itching, diarrhea, and swelling. Hydroxocobalamin is a natural form of the vitamin that your body uses more slowly, providing continuous support. It easily converts to methylcobalamin in the body.
This is the synthetic version of vitamin B12 used in supplements and in the B12 shot. Mild side effects of diarrhea and swelling can occur. Serious side effects include muscle weakness, extreme thirst, confusion, shortness of breath, headache, exhaustion, reddening of the skin, and a fast or irregular heartbeat. Very serious side effects such as chest pain and difficulty breathing are rare. You should always contact your doctor immediately if you experience any of these reactions. Contact your doctor immediately if you experience any symptoms of allergic reaction such as itching, swelling, severe dizziness, rash, or difficulty breathing after receiving a B12 shot. The best way to protect against side effects is communication. Make sure your doctor knows all the medications and drugs (including alcohol) you may have taken prior to getting the shot. Information on your family’s medical history also helps.
Everything You Need to Know About Vitamin B12
Length: 51 minutes
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Do you get B12 shots? What has your experience been? Let us know!
- Thakkar K1, Billa G2. Treatment of vitamin B12 deficiency-Methylcobalamine? Cyancobalamine? Hydroxocobalamin?-clearing the confusion. Eur J Clin Nutr. 2014 Aug 13. doi: 10.1038/ejcn.2014.165.
†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.