Does Cyanocobalamin Turn to Cyanide? Separating Fact from Fiction

October 9, 2025 •

4 min read

Up to 80% of absorbed cyanide from food is metabolized by the liver for safe excretion. This natural detoxification process also handles the minuscule amount of cyanide in cyanocobalamin, a common form of vitamin B12 found in supplements and fortified foods.

Quick Summary

While cyanocobalamin does contain and release a trace amount of cyanide during metabolism, the body safely detoxifies and excretes it, making it non-toxic for healthy individuals.

Key Points

Small, Non-Toxic Amounts: Yes, cyanocobalamin releases a minute amount of cyanide, but the quantity is thousands of times lower than toxic levels and easily managed by the body.
Efficient Detoxification: The body's natural detoxification processes, primarily in the liver, effectively convert and excrete the cyanide without harm.
More Cyanide in Food: Many common foods like almonds and spinach contain significantly higher levels of natural cyanide than a typical B12 supplement.
Synthetic B12 is Stable: The cyanide group in cyanocobalamin makes it a very stable form of B12, which is why it is commonly used in supplements and for food fortification.
Kidney Disease Precaution: Individuals with impaired kidney function may need to consider alternative B12 forms, as their ability to clear the cyanide may be reduced.
Safe for Healthy People: For the vast majority of healthy people, cyanocobalamin is a safe and effective way to supplement vitamin B12.

The Simple Answer: Yes, But It's Not What You Think

Yes, the synthetic form of vitamin B12 known as cyanocobalamin does contain a cyanide molecule. During metabolism, this cyanide group is cleaved from the cobalamin molecule so the body can utilize the vitamin. However, the key takeaway is that the amount of cyanide is extremely small and is not toxic to healthy people. The human body is naturally equipped to handle and detoxify this minimal amount of cyanide. Rumors suggesting that cyanocobalamin is a secret toxin or that it accumulates dangerously in the body are unfounded and contradict the overwhelming consensus of scientific and medical research. Concerns are often fueled by individuals promoting other, often more expensive, B12 supplement forms.

How the Body Handles Cyanocobalamin

When you ingest a cyanocobalamin supplement, it undergoes a metabolic process to become an active form of vitamin B12 that the body can use. Here is a step-by-step overview:

The cyanocobalamin molecule enters the digestive system.
During cellular absorption, the cyano group (the cyanide molecule) is removed from the cobalamin.
The cobalamin is then converted into the active coenzyme forms needed by the body: methylcobalamin and adenosylcobalamin.
The released cyanide ion is quickly and efficiently converted by the enzyme rhodanese into a harmless compound called thiocyanate. This conversion happens primarily in the liver.
The resulting thiocyanate is water-soluble and is harmlessly excreted from the body in the urine.

Cyanocobalamin vs. Naturally Occurring Cyanide

For context, the trace amount of cyanide from a typical cyanocobalamin supplement is dwarfed by the cyanide content found in many foods you consume regularly. The body's detoxification system is constantly at work processing small amounts of naturally occurring cyanide from plant sources.

Examples of Natural Cyanide Sources

Almonds: Especially bitter almonds, but even sweet almonds contain higher amounts of cyanide than a B12 supplement.
Spinach: This leafy green vegetable contains a low, natural amount of cyanide.
Apple seeds: Like the seeds of other stone fruits, apple seeds contain cyanogenic glycosides that can release cyanide if chewed.
Cassava root: A staple food in many parts of the world, it contains high levels of cyanogenic compounds that are mostly removed during proper preparation.

When Could Cyanocobalamin Pose a Risk?

For the vast majority of people with healthy liver and kidney function, the cyanide from cyanocobalamin poses no risk. However, there are limited exceptions:

Impaired Kidney Function: Individuals with chronic kidney disease may have a reduced capacity to process and excrete toxins. Some studies suggest that high-dose cyanocobalamin could potentially be harmful in this population, and alternative B12 forms might be more suitable.
Tobacco Amblyopia: This rare condition, which can cause vision damage, is often linked to smoking and is thought to involve chronic cyanide exposure. In these cases, treatment typically involves hydroxocobalamin to help clear the excess cyanide.
Defective Cyanide Metabolism: Very rare cases of metabolic disorders can affect the body's ability to handle cyanide. For the general population, however, this is not a concern.

Comparing Cyanocobalamin to Other B12 Forms

There are several forms of vitamin B12 available, each with unique properties. While marketing often promotes one form as superior, the reality is more nuanced. The most important factor for most people is simply getting enough vitamin B12, regardless of the form.


Feature	Cyanocobalamin	Methylcobalamin	Hydroxocobalamin
Cyanide Presence	Yes, contains a cyanide molecule	No, contains a methyl group	No, contains a hydroxyl group
Origin	Synthetic, created commercially for stability	Primarily naturally occurring in foods	Natural form produced by bacteria
Bioavailability	Well-absorbed, though some studies suggest lower retention	High bioavailability and generally well-retained	Excellent bioavailability and longer retention
Cost	Generally the most affordable form	More expensive than cyanocobalamin	Can be more expensive, especially in injectable form
Usage	Common in supplements, fortified foods, and injections	Growing in popularity as a supplement	Standard for B12 injections in many countries; used as cyanide antidote
Stability	Highly stable and durable for long-term storage	Less stable than the cyano form	Less stable and requires different handling

Conclusion

While it is technically true that cyanocobalamin releases a trace amount of cyanide, suggesting it is a toxic substance is misleading and scientifically inaccurate. The amount of cyanide released is insignificant and is readily detoxified by the body's natural processes, which are constantly handling far greater amounts from common dietary sources. For the average, healthy individual, cyanocobalamin is a safe, effective, and cost-efficient option for B12 supplementation. However, those with specific health conditions like impaired kidney function should consult a healthcare provider regarding the most suitable form of B12 for their needs. Ultimately, the fear surrounding cyanocobalamin is based on a misunderstanding of dosage and the body's natural defense mechanisms.

Visit the NIH for more information about Vitamin B12.

Frequently Asked Questions

No, for healthy individuals, the minuscule amount of cyanide released during the metabolism of cyanocobalamin is easily and safely processed by the body's natural detoxification mechanisms and excreted in the urine.

The body's liver contains an enzyme called rhodanese that converts cyanide into a less toxic compound, thiocyanate, which is then excreted through the urine.

Yes, other forms include methylcobalamin and hydroxocobalamin. Hydroxocobalamin is even used as an antidote for cyanide poisoning because it binds to cyanide and converts it into cyanocobalamin for safe excretion.

The amount of cyanide in a typical cyanocobalamin supplement is substantially lower than the amount of naturally occurring cyanide found in many common foods, such as almonds, spinach, and apple seeds.

People with impaired kidney function should consult a doctor before taking high-dose cyanocobalamin, as their ability to process and excrete the cyanide may be compromised.

Cyanocobalamin is the most common form because it is the most stable and cost-effective. It is also well-studied and safe for most people, making it a reliable choice for supplementation and food fortification.

For most healthy individuals, both forms are effective at treating B12 deficiency. Claims that methylcobalamin is universally 'superior' are often marketing tactics, as the body can convert both forms into the active coenzymes it needs.