The amount of time that the effects of a vitamin B12 injection will last depends on a number of factors, such as a person’s metabolism and how often the injections are administered. In general, the effects of vitamin B12 injections can last about one week; however, it’s important to consult a healthcare provider to determine how you should administer the injections. Before recommending an appropriate vitamin B12 dosage, a healthcare provider may consider other factors like your current medical condition and diet. Continue reading to learn more about how long a vitamin B12 injection lasts. 


Compared to an oral vitamin B12 tablet, a vitamin B12 injection solution does not pass through the digestive system to be processed. Instead, it is rapidly absorbed by the body within minutes after its administration. The majority of injected solution may be eliminated within eight hours after administration. Generally speaking, around 50 to 98% of the vitamin B12 taken is excreted from the body 48 hours after injection. Other studies have shown that vitamin B12 has a half-life of around six days in the blood, which means that it would take six days before half of the administered amount is excreted from the body. 


The body uses vitamin B12 for different reasons. Vitamin B12 is involved with the generation of energy, production of red blood cells, and support of healthy nerve functioning. After an injection with vitamin B12, the body immediately starts to distribute it throughout the body to be used. Excess vitamin B12 is delivered to the liver and stored. If you were to ask how long vitamin B12 injections last, the answer can be indefinite especially if you have a steady supply of it. The liver is a primary storage unit for vitamins, such as vitamin A, D, E, K and B12.

How Often Do You Need a Vitamin B12 Injection?

The usual frequency for intramuscular doses of B12 shots is every 10 days, followed by maintenance doses at varying intervals. After this period, you may be able to administer the injection once per month. This frequency is enough to reverse the signs of vitamin B12 deficiency. While taking the vitamin, it is also important to keep up with a proper diet to meet your body’s nutritional needs. 

Vitamin B12 can be found in the form of cyanocobalamin, hydroxocobalamin, and methylcobalamin. Each of these forms may have different indications and uses. Consult your doctor on the most appropriate formulation for your condition. 

Can a Vitamin B12 Injection Lead to Overdose?

Vitamin B12 overdoses are rare. Vitamin B12 has a low level of toxicity as a water-soluble vitamin that is excreted through the urine. However, certain people with kidney problems may be at a higher risk of toxicity since they may be unable to effectively eliminate vitamin B12 from the body. It is recommended to take the injections as prescribed by your healthcare provider. This way, you do not put unnecessary strain on your body and you benefit from the vitamin b12 injections

Currently, there are standard doses of vitamin B12 recommended by many healthcare professionals. For people with problems absorbing the vitamin, pregnant women, and individuals suffering from mild deficiency, a 1000 mcg dose may be recommended. Those with severe deficiency may require a 5000 mcg dose. A healthcare provider will recommend the appropriate dosage based on your overall condition. 

How Long Before a Vitamin B12 Shot Gives Results?

The effect of vitamin B12 can often be noticed within two or three days, and maximum benefits may be seen with continued use after more than three months. You may start feeling better and more energized after a course of vitamin B12. Depending on your condition, you could experience effects sooner or later than average. 

How Much Does a Vitamin B12 Injection Cost?

Now that you know how long a vitamin B12 injection lasts, you might be interested in how much it costs. The cost depends on your location and whether you do a self-injection or you get a professional to do it for you. As you start treatment, the help of a professional may be needed to properly administer the injection. But as you become more accustomed to the process, you can learn to inject the B12 on your own. You may be able to buy vitamin B12 injections online for self administration. Make sure you follow your provider’s directions before starting self-administered injections. 

Take Away

A vitamin B12 injection is absorbed in the blood within minutes after administration. It can stay in its active form for 48 hours. Excess amounts of vitamin B12 can either be stored in the liver or excreted in the urine. The effects of B12 injections are often felt within a week of use while maximum benefits may be experienced after 3 months of use. In order to get the most from your shots, it is best to consult a doctor before starting your treatment regimen. 

The experts at Medical Weight Loss Centers of America are available to answer any questions you may have about vitamin B12. A provider can evaluate your current condition to determine the appropriate dosage and formulation of vitamin B12 for you. Contact the team for more information.