Vitamin B12 Dosage Guide for Adults - GoodRx (2024)

Vitamin B12 is an important nutrient for keeping your cells healthy and working properly. But if your vitamin B12 levels fall too low, you can develop anemia and nerve damage. This can make you feel weak, tired, and irritable. It can also cause pins and needles sensations in your hands and feet.

If your vitamin B12 levels are consistently low, your healthcare provider may recommend a prescription vitamin B12 supplement (cyanocobalamin, Dodex, Nascobal) to raise your levels to a normal range. But what’s the right dose of vitamin B12, and is there a difference between the prescription and over-the-counter (OTC) versions?

What forms does prescription vitamin B12 come in?

Prescription vitamin B12 comes as an injectable liquid and a nasal spray.

You can inject vitamin B12 under the skin (subcutaneously) or into the muscle (intramuscularly, IM). Your healthcare provider may give you an injection in the office. But they may also teach you how to inject it yourself at home.

The injection comes in 1 mL, 10 mL, and 30 mL vials that contain 1,000 mcg of vitamin B12 per mL. You should store the vials at room temperature in an area that’s protected from direct light.

Nascobal is a prescription vitamin B12 nasal spray. It contains 500 mcg of vitamin B12 per spray. Unlike most other nasal sprays, Nascobal should not be primed before you use it. Each device only contains one dose of medication, so you’ll waste your dose if you try to prime it first.

It’s best to blow your nose before each dose of Nascobal. Then, gently close one nostril with a finger. Insert the Nascobal device into your other nostril while tilting your head forward. Close your mouth, breathe in gently through your nose, and press the plunger to administer one spray of medication.

Don’t use Nascobal within one hour before or after consuming hot foods or liquids. They can make your nose run, which prevents the medication from absorbing properly. If you have nasal congestion or a runny nose, you may need to wait until your symptoms resolve to use Nascobal.

What’s the typical prescription vitamin B12 dosage for adults?

The vitamin B12 dosage for adults with consistently low levels depends on the dosage form you’re using. If you have severe symptoms of vitamin B12 deficiency, your healthcare provider will likely recommend injectable vitamin B12. That’s because injections help get your vitamin B12 levels up to where they should be faster than other dosage forms.

If your levels are only slightly low, or you don’t have symptoms, your healthcare provider may have you try an OTC form of vitamin B12 first. But if you can’t absorb oral vitamin B12 properly, you’ll likely need prescription vitamin B12 treatment.

Good to know: For people who can’t absorb vitamin B12 from their diet or oral tablets, prescription vitamin B12 treatment is usually a lifelong medication.

Cyanocobalamin injection

The FDA-approved injectable vitamin B12 dosage for adults is 100 mcg (0.1 mL) daily for 6 or 7 days. From there, the dosage can be extended to 100 mcg every other day for 14 days (7 doses), then every 3 to 4 days for several more weeks. Once your vitamin B12 levels have stabilized, it’s recommended to continue with 100 mcg once a month.

But many healthcare providers follow a different dosing schedule for injectable vitamin B12. It’s more common to inject 1,000 mcg (1 mL) once daily for 1 week. Then you’ll inject 1,000 mcg once weekly for 1 month, followed by once-a-month injections thereafter.

Nascobal nasal spray

The approved vitamin B12 dosage for Nascobal is 500 mcg (one spray) in just one nostril once a week. Your healthcare provider may increase the dose depending on your vitamin B12 blood levels after one month.

Good to know: Nascobal isn’t approved for severely low vitamin B12 levels. But once your levels have been returned to normal with injectable vitamin B12, Nascobal may be an option for you as an alternative to monthly injections.

What’s the typical OTC vitamin B12 dosage?

The recommended daily intake of vitamin B12 for most adults is 2.4 mcg. Many people can easily meet this through a balanced diet that includes animal-based foods such as meat, fish, and dairy products.

But you may have trouble meeting the daily vitamin B12 requirement if you’re vegetarian or vegan. People with conditions such as celiac and Crohn's disease or those who’ve undergone weight-loss surgery may also have trouble absorbing vitamin B12 properly.

Vitamin B12 is available OTC in oral tablets as well as liquids and dissolvable tablets that you place under your tongue. One form doesn’t seem to work better than another.

When it comes to the right dosage, it’s best to discuss that with your healthcare provider. It’s only necessary to take extra vitamin B12 if your blood levels are low. If you take more than you need, your body will just get rid of the extra when you pee.

If your vitamin B12 levels do come back low, your provider can guide you as to what form and dosage of vitamin B12 is best. They may have you try an oral OTC vitamin B12 supplement first before trying a prescription form.

What happens if you miss a dose of vitamin B12?

If you miss a daily dose of vitamin B12, take it as soon as you remember. But if it’s close to your next scheduled dose, skip the missed dose and take only the regular dose. Don’t take two doses at the same time.

If you only use vitamin B12 once a week or once a month, and you take your dose a day or two later than usual, you may need to adjust the day of the week or month you take it moving forward. Reach out to your healthcare provider or pharmacist for guidance if this happens.

It can be difficult to remember a medication if you don’t take it every day. So you may want to consider a medication reminder app or something similar to help you.

What should you do if you take too much vitamin B12?

Vitamin B12 is a very safe medication. As mentioned, your body gets rid of any extra through your urine. So too much vitamin B12 isn’t likely to cause you any harm. In rare cases, injectable vitamin B12 can cause skin irritation or rosacea, but this isn’t a common side effect.

Keep in mind that taking more vitamin B12 than you should won’t give any added benefit, either. So it’s best to stick to your prescribed dosage, and ask your healthcare provider if you have any questions or concerns about how much you’re taking.

How to save on prescription vitamin B12

There are many ways to save on vitamin B12 medications. Nascobal is only available as a brand-name medication. But you can find cyanocobalamin injections as a lower-cost generic.

GoodRx can help you save over 80% off the average retail price of generic injectable cyanocobalamin. The price at certain pharmacies is as low as $12.46 with a free GoodRx discount.

If you have commercial insurance and meet eligibility requirements, Nascobal’s price is as little as $0 using a savings card from the manufacturer.