Shots of vitamin B12 are often given in doses of 1,000 mcg/mL, while vitamin B12 pills often come in capsules, tablets, or soft gels of 50 to 5,000 mcg. But you can’t just make B12 pills equal the dosage of a B12 shot.
Vitamin B12 is essential for keeping your central nervous system healthy, making red blood cells, and creating DNA. (Kind of a big deal!) And if you have a deficiency, taking B12 pills or getting a B12 shot are both legit ways to up those B12 levels.
Here are the dosages you can expect from different B12 options.
While it might seem like a 1000 micrograms (mcg) B12 shot is equal to a 1,000 mcg B12 supplement, it’s not that simple.
Your body absorbs these B12 formulations differently, so you can’t simply make B12 pills equal a shot dosage. How often you take B12 pills and get B12 shots also differs.
For B12 deficiency, a typical injection dose is 1,000 mcg once a week for 4 to 8 weeks and then 1,000 mcg once a month. But dosages can vary depending on if you’re treating severe, mild, or asymptomatic B12 deficiency.
For vitamin B12 pills, most people take these daily in doses recommended by their doc but taking 1,000 mcg daily is pretty standard. However, an oral B12 dose is often larger because your body usually doesn’t absorb it all.
According to 2008 research, your body only absorbs about 1.3 percent of a 1,000 mcg oral dose and 2 percent of a 500 mcg oral dose. The same study found injection absorption rates were about 55 to 97 percent. B12 injections are intramuscular shots (meaning they go into the muscle), which are absorbed rapidly because of the great blood supply in the muscle.
Taking B12 supplements can be an effective way to treat B12 deficiencies and isn’t necessarily inferior to B12 shots. If you’re deficient, your doc may recommend you take about 1,000 to 2,000 mcg of vitamin B12.
In a 2018 review, researchers found evidence that taking 1,000 mcg of B12 and getting B12 injections had similar effects on treating B12 deficiencies. But the studies included were small and only lasted about 3 to 4 months.
Older research also supports that taking 1,000 to 2,000 mcg of B12 is likely just as effective in treating deficiencies as injections.
You can totally take B12 pills instead of injections if your doc gives you the A-OK! Only people with vitamin B12 deficiencies should take oral B12 supplements (that’s about 6 percent of the US population under age 60).
Even though you can find B12 in supplement aisles, you really need to make sure you’re actually deficient before taking B12 supps. Taking B12 capsules when you’re not deficient can lead to side effects, have virtually no benefits, and just be a waste of $$$.
Based on the research we have so far (from 2005 and 2018) it looks like supplements are pretty effective at normalizing B12 levels at doses of 1,000 to 2,000 mcg. But you’ll want to work with a pro to come up with a plan.
You need to go to a doctor to get a prescription for B12 injections. Typically, a healthcare professional will inject them for you, but you can also sometimes do them at home. Talk with a pro to figure out what’s right for you.
B12 shots are made from hydroxocobalamin or cyanocobalamin, manufactured forms of vitamin B12. They’re intramuscular injections, which means they’re injected into the muscles — typically in your arm or thigh.
With the shot, the B12 is absorbed rapidly thanks to the blood supply in the muscle and you should experience benefits right away. Within a couple of days, you might start to see your symptoms improve and feel better.
But B12 injections aren’t just a one-and-done thing. You’ll usually start getting injections at least a few times a week. Then, your dose may change based on your doc’s orders and how you respond to treatment. As your symptoms improve, you might only need them every couple of months.
If you’re heading to the doctor to get a B12 shot, there’s no need to prepare. Before you get one, you’ll discuss the process and your history of meds and allergies to make sure you’re good to go.
If you’re giving yourself the shot at home, your doc will tell you how to prep and administer it. You’ll need to:
- Clean the injection area with rubbing alcohol.
- Administer the injection into the muscle (the thigh is typically easiest if you’re doing it yourself).
- Dispose of the needle properly (in a sharps container, and not in your regular garbage — return it to the doc’s office or a biohazard collection site!)
After the B12 shot is injected into your upper arm, thigh, hip, or butt, you should experience benefits right away.
After the shot, many people experience side effects like pain, itching, and swelling. But these effects should go away pretty quickly.
When you first start getting the shots, your doc will prob prescribe an injection at least a few times a week.
Your dose may change depending on how you respond to the treatment and the vitamin B12 levels in your blood.
As your symptoms improve, you might only need them every few months or so.
Both B12 shots and pills have pros and cons. So, when picking between them, it really comes down to your preferences and what your doc recommends. Here are the main differences:
- Cost and convenience. B12 pills are much cheaper than injections. You can get a bottle of 100 for under $10, at just 10 cents a serving. Meanwhile, one injection of B12 will vary widely based on health insurance but can easily be more than $50. You’ll also need to make an appt, get bloodwork done, and get a prescription from your doc.
- Absorption. B12 injections are absorbed straight into your bloodstream, making them faster-acting and potentially more effective. Though the science hasn’t proven how effective the pills are for sure yet, experts *do* know that injections really work — and fast. Also, keep in mind that under-the-tongue supps may be more effective.
- Mode of application. Some people are needle-phobic — others hate remembering to take pills every day. Ultimately, the choice is up to you (and your doc).
B12 injections might not be ideal if you:
- have had an allergic reaction to hydroxocobalamin or any other meds in the past
- have low levels of potassium
- have an irregular or rapid heartbeat
Again, don’t just start taking B12 if you don’t know you’re deficient. Signs of a B12 deficiency include:
- difficulty walking
- uncontrollable muscle movements
- confusion, forgetfulness, or memory loss
- changes in mental state or mood
- changes in smell or taste
- vision problems
- weight loss
- glossitis, aka a painful, smooth, and red tongue
If you have any of the above symptoms, talk with a doc.
According to the National Institutes of Health (NIH), vitamin B12 hasn’t been proven to cause any serious harm, even at high doses. That being said, taking the supplements when you don’t need them may cause side effects like:
Serious side effects of the shot are rare, but may include:
- skin rash or hives
- muscle weakness
- dizziness and fatigue
- feeling super thirsty
- frequent peeing
- a fast or irregular heart rate
- swelling of your arms or legs
If you notice any side effects of the pill or shot, call your doc right away.
Both B12 vitamins and injections can help treat a B12 deficiency, although your body will absorb injections much quicker and more easily.
We need more evidence to know if the pills are as effective as the shots over time, though some research suggests they work, especially when it comes to sublingual supps. As of now, the pros say they’re a suitable replacement.
If you think you’re low on B12, talk with your doc.