Vitamin B12 injections: what the label says they are for, who is deficient and the risks

A B12 shot is an injection of vitamin B12, usually as cyanocobalamin. The FDA-listed label for the prescription injection gives one use: vitamin B12 deficiency caused by problems absorbing it.¹

Med spas often offer these shots for energy. The label and the National Library of Medicine's MedlinePlus list no energy use. Here is what they do say, who tends to be low in B12, and what to ask. It gives no dose. Whether you need B12 is a question for a clinician.

What B12 is

Vitamin B12 is a water-soluble vitamin that helps form red blood cells and maintain the nervous system. The body stores a few years' worth in the liver, and what it doesn't use leaves in the urine.² It is found naturally in animal foods such as fish, meat, poultry, eggs and dairy, and in fortified cereals and some nutritional yeast products.²

What the label says the injection is for

The label says cyanocobalamin injection is for vitamin B12 deficiencies due to malabsorption, which may be associated with these conditions.¹

The label adds that higher-than-normal needs, such as in pregnancy, an overactive thyroid, anemia from red cell breakdown, bleeding, cancer, and liver and kidney disease, can usually be met with oral supplements.¹ It also says the injection is suitable for the B12 absorption test.¹

Who tends to be low in B12

MedlinePlus says deficiency happens when the body doesn't get or can't absorb enough B12. It is most common in people over the age of 50 and in the other groups below.²

The label says a deficiency left to progress for more than 3 months may cause permanent degenerative changes in the spinal cord.¹ The label warns that indiscriminate use may mask the true diagnosis, so ask whether your B12 level has been checked.¹

Warnings on the label

The label says cyanocobalamin is contraindicated in people with sensitivity to cobalt or to vitamin B12. It warns that anaphylactic shock and death have been reported after injected B12. It also warns of rapid optic nerve damage in people with early Leber's disease, an inherited eye condition, and of low potassium and sudden death when severe anemia is treated intensely.¹

Reported side effects include itching, a short-lived rash, mild diarrhea and a feeling of swelling of the whole body. Fluid in the lungs, heart failure early in treatment and blood clots in the peripheral vessels have also been reported.¹

The label says to avoid the intravenous route, because almost all the vitamin is lost in the urine when it is given that way.¹ That matters if a B12 shot is offered on an IV menu. See our IV therapy page.

Pernicious anemia

The label says people with pernicious anemia need injections of B12 for the rest of their lives, and that without them the anemia returns and nerve damage can follow. It says folic acid can prevent the anemia while the nerve damage progresses, so it shouldn't be taken instead.¹ That is a condition for a doctor to manage.

What to ask a clinic

The label we read is a prescription label, and a med spa may use a different product, or a compounded one. Which licensed professionals may give an injection depends on your state. See our guide to who may inject.

Here is what to bring to a consultation.

Cost

We don't give prices on this page.

Common questions