types of B12

Methylcobalamin vs Cyanocobalamin B12

Vitamin B12, also known as cobalamin, is an essential water-soluble vitamin that performs several functions in the body. It's responsible for DNA synthesis, red blood cell production, and neurological function.

B12 is found naturally in many animal products like meat, fish, and certain cheeses, but its animal-based sources make plant-based eaters susceptible to a deficiency. Getting older is another risk factor, as we produce less of a protein called "intrinsic factor" that's necessary for absorption.

Symptoms of low B12 include fatigue, poor balance, difficulty concentrating, changes to mood, and jaundice. You can read more about signs of a deficiency here. It can be difficult to catch some of the more subtle signs of deficiency, but a blood test can confirm whether your levels are low.

Because B12 deficiencies are so common, many people choose to supplement as a convenient at-home alternative to B12 injections.

When you're on the hunt for a B12 supplement, you'll usually see two main forms listed on labels: cyanocobalamin, and methylcobalamin.

We'll explore these two types of B12 as well as the other two you won't see as often, and tell you the difference between methylcobalamin vs cyanocobalamin and when you might want to take each, discuss cyanocobalamin vs hydroxocobalamin, methylcobalamin vs adenosylcobalamin, and when you need each, as well as the best form of B12 for absorption.

What are the types of B12? 

Exploring B12 Methylcobalamin, Cyanocobalamin, Hydroxycobalamin, and Adenosylcobalamin.

Four types of B12: methylcobalamin, cyanocobalamin, hydroxocobalamin, adenosylcobalamin

There are four types of B12: methylcobalamin, cyanocobalamin, hydroxocobalamin, and adenosylcobalamin. You'll typically only find methylcobalamin and cyanocobalamin on over-the-counter supplement labels.

Each -cobalamin molecule consists of an atom of the metal cobalt surrounded by a corrin ring (meaning it's the "core" of the B12). It's attached to another molecule: cyanide in cyanocobalamin, a methyl group (-CH3) in methylcobalamin, a hydroxyl group (-OH) in hydroxocobalamin, and an adenosyl group in adenosylcobalamin (-C15H22N6O5S).

B12 Methylcobalamin

B12 Methylcobalamin, the form used by Why Not Natural, is a naturally-occurring coenzyme found in many animal products. It's the best form of B12 for absorption as your body can use it directly which is what makes it an excellent choice for supplementation. 

This is the most active form for supplementation as well (the two active forms in the body are methylcobalamin and 5-deoxyadenosylcobalamin), and your body uses it in the liver, the brain, and the nervous system.

It's the best option for people who have a methylation defect because it's a coenzyme for the methylation cycle, a process responsible for many important functions in the body (including but not limited to DNA synthesis, immune function, hormone regulation, and detoxification).

It should be used in combination with one of the other 3 forms so that adenosylcobalamin is consumed as well, and Why Not Natural's B12 naturally contains hydroxocobalamin in addition to methylcobalamin for B12 synergy! (1)


Cyanocobalamin, the cheapest form of B12, has been the most common supplement form for many years. It is also the form used to fortify food. The reason it's so commonly used is because the cyanide molecule gives it extra stability.

However, it's the only form that is not found in nature, aside from trace amounts found in human tissues from cyanide intake due to smoking or other exposure.

Cyanocobalamin was shown to be absorbed slightly more than methylcobalamin in one study, however, it was then shown in another study that three times more cyanocobalamin was excreted in urine compared with methylcobalamin. (2,3)

This means that cyanocobalamin is less able to be stored than methylcobalamin. However, it can be used in addition to methylcobalamin as it can convert to both methylcobalamin and adenosylcobalamin in the body. 

For those with a MTHFR gene deficiency, cyanocobalamin is not a good option as it requires conversion.

Cyanocobalamin vs hydroxocobalamin

Hydroxocobalamin is not mentioned often when comparing B12 forms because it's typically inaccessible to the general public, as it's the most expensive form and usually only available by prescription. It's also used to treat cyanide poisoning!

Hydroxocobalamin can convert to both adenosylcobalamin and methylcobalamin in the body, like cyanocobalamin. However, unlike cyanocobalamin, it's a naturally-occurring form that is produced by bacteria in the digestive tract when breaking down foods. It can also be produced in a laboratory in a process that mimics this.

If you're consuming the Why Not Natural B12 supplement, you're getting a bonus of hydroxocobalamin. Keep reading to learn more about this!

Methylcobalamin vs adenosylcobalamin

Adenosylcobalamin is another naturally-occurring co-enzyme like methylcobalamin. It's not often discussed, but it's very important!

Methylcobalamin and adenosylcobalamin do many of the same functions, but adenosylcobalamin additionally supports mitochondria (the "powerhouses of the cells"). This keeps them functioning optimally.

It's the least stable form of B12, which is why you won't find it available in many supplements. 

It's recommended to consume methylcobalamin along with either adenosylcobalamin, hydroxocobalamin, or cyanocobalamin to benefit from methylcobalamin-adensosylcobalamin synergy. You can consume a supplement like Why Not Natural B12 that contains both methylcobalamin and naturally-occurring hydroxocobalamin.

Why Not Natural B12 Contains Hydroxocobalamin

While we don't advertise it among the many benefits of our B12 supplement, the Why Not Natural B12 contains the full listed dose of methylcobalamin with added hydroxocobalamin! This additional hydroxocobalamin is naturally-occurring and results from the methylcobalamin extraction process. It's completely vegan, just like the methylcobalamin.

You can see the results of our most recent laboratory tests below:

 Why Not Natural methyl B12 with hydroxocobalamin

The results are for one 1 mL serving and show that each serving contains a little over 50,000 mcg of methylcobalamin (the listed dose) and an additional 16,000 mcg of hydroxocobalamin!

Taking the Why Not Natural B12 allows you to experience the synergistic effects of methylcobalamin and hydroxocobalamin, which converts to adenosylcobalamin in the body.

And don't worry- there's no upper limit on B12, so you can take it safely at any dose. (4) While the RDI is set at a mere 2.4 mcg-2.8 mcg per day as a minimum, experts recommend at least 1000 mcg-1500 mcg per day for those under 65 (more for those over). (5) 


(1) Treatment of vitamin B12 deficiency-methylcobalamine? Cyancobalamine? Hydroxocobalamin?-clearing the confusion

K ThakkarG Billa

(2) Absorption of cyanocobalamin, coenzyme B 12 , methylcobalamin, and hydroxocobalamin at different dose levels

J F AdamsS K RossL MervynK BoddyP King


(3) Intestinal absorption and concurrent chemical changes of methylcobalamin

K OkudaK YashimaT KitazakiI Takara

(4) https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/#h3

(5) https://www.sciencedirect.com/science/article/pii/B978032335868200013X

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1 comment


My mother has been given synthetic Hydroxocobalamin by injection for quite some time now. I am not happy about the possible build up of side effects, as she has developed wheezing after taking it. Is is safe to use a natural B12 instead? If so, how would I explain this to the NHS as they are always trying to push drugs on her and seem to be annoyed that I have managed to look after her without their involvement and I only use natural vitamins and minerals and she is in pretty good condition, I just don’t trust Big Pharma in the slightest.

Many thanks.


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