syringes laying flat on a table

How Quickly Do B12 Shots Work?

What the shots are good for, who should consider taking them, and how to give yourself a jab.

Fast Facts

  • B12 injections can be more effective than pills in certain patients who have trouble absorbing vitamin B12.
  • Vitamin B12 can be injected just under the skin, or directly into the muscle.
  • It can take up to a day to feel the effects of vitamin B12 shots, though some people notice the effects sooner.

Look down the ingredient list of any multivitamin bottle and you’ll probably find B12. But this buzzy vitamin—prized for its ability to boost energy and mood—isn’t just available in pill form. Vitamin B12 injections are also gaining in popularity and availability. Curious about the benefits of B12 shots and whether they can give you a lift? 

About six percent of Americans under the age of 60—and 20 percent of those over 60—have a B12 deficiency (1). And while eating B12-rich foods and take oral supplements can boost your levels, vitamin B12 injections are an increasingly popular way to supplement. 

Vitamin B12 is responsible for making red blood cells, white blood cells, and platelets. It may also enhance the activity of certain immune cells, which may ward off viruses and chronic disease such as cancer, according to a 2020 review in the medical journal, Nature (2).

For people who don’t absorb B12 well, or those whose want to make sure beyond reasonable doubt that they’re getting an ample dose quickly, B12 shots are available via prescription, says Richard Foxx, M.D., a board-certified physician who treats hormonal disorders and nutritional deficiencies.

B12 Shots

Vitamin B12 is a water-soluble B vitamin found in some foods. Most are animal sources (milk, egg yolks, yogurt, salmon, tuna, beef) which is why vegetarians and vegans have a higher risk of being deficient (3). B12 is also added to certain foods, like cereals.

B12 injections are especially useful for people with a B12 deficiency, which tends to stem from difficulties absorbing the nutrient, not falling short nutritionally, says Foxx. People with stomach and intestinal conditions such as celiac disease and Crohn’s disease may struggle to absorb enough B12 from their food.

Aging can also set you up for a B12 shortage since absorption declines as you get older.

If you’re experiencing symptoms of B12 deficiency, your doctor may order a blood test. If your blood levels are lower than 200pg/mL or if you are diagnosed with pernicious anemia, your doctor may recommend B12 supplementation via injection.

If your levels are in the intermediate range, your doctor may also test your levels of MMA and homocysteine. These blood tests can help determine if you’re low on B12 (6).

Signs that you’re not getting enough B12:

Vitamin B12

Vitamin B12 Benefits

B12 is linked to several important functions in the body, including:

Red blood cell formation

Your body needs B12 to produce healthy red blood cells. Low vitamin B12 levels cause a reduction in red blood cell formation and prevent them from developing properly. If you don’t have enough red blood cells, you may develop a medical condition called pernicious anemia. (1)

DNA synthesis

Your body also needs B12 to form DNA (1). It’s also important for the formation of brain and nerve cells.


Evidence has linked depression with B-12 deficiency. One study reported that vitamin B12 deficiency was associated with twice the risk of severe depression (4).

Bone health

A study published in the Journal of Bone and Mineral Research (5) found that low B-12 was linked with poor bone mineral density, suggesting a role for the vitamin in bone formation.

Weight loss and metabolism

Some studies suggest that higher vitamin B12 levels may protect against obesity or being overweight. For example, a 2019 study of over 9,000 adults found people with obesity had lower blood levels of vitamin B12 (8). These studies only show a link between vitamin B12 deficiencies and weight gain, Matthew Cowling, D.O., a physical medicine and rehabilitation specialist in Madison, Wisconsin who specializes in weight loss, previously told The Edge. Researchers are trying to tease out whether taking additional B12 might help people lose weight.


The research is limited and far from a slam dunk but Cowling says higher doses of B 12 supplementation may increase energy, particularly if you have a deficiency or are at risk of a deficiency .


B12 Shots Benefits

When you swallow a B12 supplement, it’s hard to know how much of the nutrient you actually absorb, says Foxx. 

B12 injections, also known as cyanocobalamin, or hydroxocobalamin, tend to be a more reliable delivery vehicle for those who require a precise dose or just want to be certain that their supplementation efforts are working. “B12 injections can be more effective than pills in  patients who have trouble absorbing vitamin B12,” says Foxx.

Another reason you might opt for vitamin B12 injections over oral supplements: B12 injections are required less frequently than oral supplements. Typically you would be a B12 injection once a week or every few weeks, says Foxx.

B12 Shots Vs Pills

How Quickly Do B12 Shots Work?

Most people report improvements in symptoms right after receiving B12 injections. But it can take anywhere from hours to a day to see B12 blood levels rise after injection, Foxx says. 

B12 Injections: How Often?

Generally, when treating a B-12 deficiency, you’ll get a 1,000-microgram shot every day or two for the first week (2).

After that, you may shift to once-a-week injections for one to two months, and then to monthly injections.

Do You Need a Prescription for B12 Injections?

Yes, you need a prescription for B12 injections. However, once you have the Rx from your healthcare professional, you don’t have to travel to his or her office for every injection. Vitamin B12 injections are available at drug stores and through Hone.

If a Hone doctor feels a prescription for B12 injections is right for you, you’ll be sent everything you need to self-inject at home.

B12 Injection Dose

A typical dose of vitamin B12 is 0.5 to 1.0 ml (or 500 to 1000 micrograms), says Foxx, but always follow your doctor’s prescribing directions.

How to Administer a B12 injection to Yourself

There are two ways to self-inject vitamin B12: Subcutaneously, or just below the skin, and intramuscularly, which goes directly into the muscle, says Foxx. Regardless of which option you choose, you’ll typically inject yourself once every one to two weeks as per your doctor’s directions.

What you’ll need

While self-injections can sound a bit scary, they’re actually not super complicated. All you need is a little courage and the following items:

B12 Injection Sites

Choose a B12 injection site that’s easy to see and access using both hands, says Foxx. You’ll want to avoid areas with bones and large visible blood vessels, like the back of your hand. He recommends one of the following locations:


For subcutaneous injections, the skin a couple of inches left or right of the belly button is ideal since it’s easy to pinch, which pulls fatty tissue away from the muscle—a good idea since you’re not aiming for the latter in this approach.


For intramuscular injections, the center of the top of the thigh is a smart place to choose since the muscle there is easily accessible. The area can also be used for subcutaneous injections.

How to Inject Vitamin B12

The injection method varies, depending on whether you are injecting B12 under the skin or directly into the muscle. If you work with a Hone physician to get vitamin B12 injections, follow their instructions about where and when to administer the jabs.

Subcutaneous Vitamin B12 Injections

  1. Wash your hands with soap.
  2. Wipe the B12 injection site with an alcohol swab to sanitize the area.
  3. Fill the syringe with B12 and remove the cap from the needle.
  4. Use the thumb and pointer finger of your non-dominant hand to pinch the skin at the injection location.
  5. Hold the syringe like a pencil in your dominant hand at a 90-degree angle to the B12 injection site, and insert the needle into the skin until you feel “a little pop,” a sign you’ve reached subcutaneous tissue.
  6. Press the plunger to release the liquid.
  7. Withdraw the needle and apply pressure to the injection site using gauze, a cotton ball, or a bandage.
  8. Dispose of the needle safely.

Don’t be surprised if you don’t see a trace of blood, says Foxx. There should be little to no bleeding since the wound will be smaller than a mosquito bite.

Intramuscular Vitamin B12 Injections

  1. Wash your hands with soap.
  2. Wipe the B12 injection site with an alcohol swab to sanitize the area.
  3. Fill the syringe with B12 and remove the cap from the needle.
  4. Relax your thigh muscle by sitting down. Squeeze the center of the muscle.
  5. Hold the needle in your dominant hand at a 90-degree angle to the injection site and insert the needle about an inch in.
  6. “Pull the syringe for 5 to 10 seconds. If you see blood in the syringe remove the needle and syringe and apply moderate pressure for about a minute. Then reinsert the needle and syringe an inch or so away from where it was before.
  7. Press the plunger to release the liquid.
  8. Remove the needle and apply pressure to the area using gauze, a cotton ball, or a bandage.
  9. Dispose of the needle safely.


Vitamin B12 may boost your energy, reduce stress, and support your brain. Connect with a Hone doctor today to see if it’s right for you. 

Side Effects from Vitamin B12 Shots

There’s no established toxic dose for B12—since it’s a water-soluble vitamin, you’ll flush out whatever you can’t use. However, you can feel mild to moderate pain in the injection site (7).

Other common side effects of B12 injections include:

If you experience any uncommon side effects, such as chest pain or hives, contact your health care provider immediately.

The Bottom Line

Vitamin B12 injections can help if your gut doesn’t absorb nutrients well or you don’t want to take a daily oral supplement. B12 can be injected just under the skin (often in the abdomen) or into the muscle (usually the thigh). Vitamin B12 injections are generally safe side effects are mild.