How Long Does It Take For a Vitamin B-12 Shot To Take Effect?

Intravenous vitamin injection therapy became famous in the US in the year 1980. This IV therapy is advantageous for people who have a problem in absorbing B-12 from the stomach. People who take certain antibiotics and stomach acid-altering medications such as H2 receptor antagonists have poor absorbing abilities. In such cases, B12 shots are the better choice and most reliable method of quickly replenishing the body’s B-12 storage and disrupt the drawback of deficiency. Generally, hydroxocobalamin in the form of injection is prescribed 6 times over 2 weeks and later once every three months. According to NHS guidelines, a patient with neurological symptoms must require more shots.

How Long Does It Take For a Vitamin B-12 Shot To Take Effect?

Types of B-12 Shots

Vitamin B12 Shots Have Been Proven Effective For Years. There Are Two Type of B12 Shots Involve: Cyanocobalamin and Hydroxocobalamin.

Cyanocobalamin is a synthetic drug, which breaks down in the body naturally to methylcobalamin and the poison cyanide. But, the quantity of cyanide is considered to be clinically irrelevant. It is affordable price and has well tolerance, but not suitable for smokers. Detoxification is difficult and not suitable.

Hydroxocobalamin is a natural form of vitamin B-12, produced by microoraganism and found in foods. It is easier to break and has no byproducts like cyanocobalamin. It is quite expensive, but has good tolerance, detoxification and better release effect.

How Long Does It Take For a Vitamin B-12 Shot To Take Effect?

Deficiency symptoms may improve within 2 to 3 days of a vitamin B12 injection. However, it depends on the person metabolic activity. The effect of B-12 shot may vary from person to person. But it is effective than oral pills even when taken in high doses might take more time for absorption. Oral drugs achieving 100% bioavailability is difficult, it decreases because of incomplete absorption and first-pass metabolism. Hydroxocobalamin stay active in the human body for much longer and is absorbed by the cells much more efficiently. The absorption of intramuscularly administered hydroxocobalamin is around three times as high as that of cobalamin and the effect lasts considerably longer too.

Vitamin B12 has the possibility to interact with certain medications, such as diabetic prescriptions, metformin, proton pump inhibitors, antagonists and antibiotics. High doses can also possibly inhibit other vitamins, enzymes and minerals, which is always a budding problem when taking any nutrient in very large quantities.

Use Cyanocobalamin Hydroxocobalamin
Replenishing the body store 5 -8 weeks, 2 x 1000 µg per week 1000 µg per week for 4 weeks or 2 x 1000 µg per week for 1-3 weeks
Maintenance therapy 100 µg every 2-3 weeks or 1000 µg per month 1000 µg every 3-6 months

Vitamin B12 Injections – The Correct Dosage

Vitamin B12 shots are above all used to rapidly refill the body store and to ensure a healthy vitamin B12 supply for people with malabsorption and particularly anemic patients. The therapy doses for some exceptional cases are listed here:

  • For pernicious anemia -100 mcg IM/SC once daily for 6 to 7 days.
  • For a hereditary condition that causes vitamin B12 malabsorption (Imerslund-Grasbeck disease) – hydroxocobalamin injected into the muscle at a dose of 1 mg daily for 10 days.
  • For cyanide poisoning: Hydroxocobalamin (Cyanokit) has been given intravenously (by IV) for a total dose of up to 10 grams.


Research studies say that the prevalence of deficiency in the UK is one in 10 people aged 75 and over, one in 20 aged 65 to 75 and prevalence is around 11% among young aged people. Over 40% of people in the U.S. are deficient in B12. Vitamin B12 shots represent an excellent alternative to oral vitamin B12 supplements for these deficient people. It is easily affordable, safe and recommended to all ages. Injections are particularly recommended in specific clinical cases of B12 deficiency because of their higher intake levels.

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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:January 16, 2024

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