Is Vitamin K Menadione? Understanding K3 and Its Differences

December 29, 2025 •

4 min read

While some people use the terms interchangeably, research from the 1980s and 1990s demonstrated that menadione, or vitamin K3, is harmful to humans. This critical distinction reveals that menadione is not a safe, natural form of vitamin K for human consumption, a misconception that has led to its ban in dietary supplements.

Quick Summary

Menadione is a synthetic form of vitamin K known as K3, distinct from the natural vitamins K1 and K2 found in foods. It is not approved for human supplements due to documented toxicity issues, though it is used in animal feed. Its presence as an intermediate in the metabolic pathway of K1 to K2 occurs naturally in the body but differs significantly from its role as a supplement.

Key Points

Menadione is synthetic: Menadione is a synthetic compound, often called vitamin K3, and is not a natural form of vitamin K like K1 and K2.
Toxic for humans: Due to documented risks of toxicity, including liver damage and hemolytic anemia, menadione is banned from dietary supplements for humans.
Used in animal feed: Menadione is used as a nutritional supplement in regulated quantities for livestock and pet food, where it does not cause the same toxicity issues.
Metabolic intermediate: The human body naturally produces small amounts of menadione as an intermediate when converting plant-based K1 into the active K2 form, MK-4, but this is a controlled process.
Focus on natural forms: For human consumption, it is safest and most effective to focus on dietary sources of natural vitamin K1 and K2 from leafy greens, fermented foods, and animal products.

Menadione vs. the Vitamin K Family: Breaking Down the Differences

To understand if vitamin K is menadione, it's essential to recognize that "vitamin K" refers to a family of compounds, not a single substance. The primary types are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone), both of which are natural and beneficial to human health. Menadione, often called vitamin K3, stands apart as a synthetic, man-made version with a different chemical structure and toxicological profile.

Vitamin K is a fat-soluble nutrient vital for several bodily functions, most notably blood clotting and bone health. The natural forms, K1 and K2, are safe and readily available through diet. K1 comes from green leafy vegetables, while K2 is found in fermented foods and animal products, and is also produced by bacteria in the gut.

The Controversial History of Menadione (Vitamin K3)

Menadione's history is marked by controversy and eventual removal from the human supplement market. Although it was once used to treat vitamin K deficiencies, studies in the 1980s and 1990s revealed significant safety concerns. It was shown to cause liver toxicity, damage to red blood cells (hemolytic anemia), and other adverse effects. The mechanism behind its toxicity involves producing harmful reactive oxygen species (ROS) that interfere with the body's natural antioxidants. As a result, regulatory bodies like the US Food and Drug Administration banned its sale as a human dietary supplement.

Conversely, the natural forms of vitamin K (K1 and K2) have a very low potential for toxicity, with no established upper intake level (UL) for healthy individuals.

How Menadione Functions in the Body (and Not as a Supplement)

An interesting aspect of menadione is its role as a metabolic intermediate in the body, which differs from its use as a supplement. Research indicates that when humans consume vitamin K1, a portion is converted into menadione in the intestines. This menadione is then further converted into the highly active MK-4 form of vitamin K2 in various tissues throughout the body, including the brain, pancreas, and testes. This natural process is tightly regulated, preventing the accumulation of toxic levels of menadione. This is completely different from introducing high doses of synthetic menadione directly into the body via a supplement, which bypasses the body's natural regulatory and protective mechanisms.

Comparison of Vitamin K Forms


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)	Vitamin K3 (Menadione)
Source	Plants, especially leafy greens (e.g., spinach, kale).	Fermented foods (e.g., natto), animal products, and produced by gut bacteria.	Synthetic, manufactured in a lab.
Human Supplement	Yes, widely used and considered safe.	Yes, widely used and considered safe.	No, banned for human supplements due to toxicity.
Toxicity	Low potential for toxicity.	Low potential for toxicity.	High potential for toxicity at high doses; linked to hemolytic anemia and liver damage.
Function	Essential for liver production of clotting factors.	Plays roles in bone and cardiovascular health; also contributes to blood clotting.	Metabolically converted into vitamin K2 (MK-4) within the body but is toxic as a direct supplement.
Water/Fat Solubility	Fat-soluble.	Fat-soluble.	Water-soluble (often used as menadione sodium bisulfite).

Natural Sources of Safe Vitamin K

Instead of seeking out menadione, individuals should focus on a diet rich in the natural and safe forms of vitamin K. The good news is that these are abundant and easy to incorporate.

For Vitamin K1: Simply include more green leafy vegetables in your meals. Excellent sources include spinach, kale, broccoli, and Brussels sprouts. Cooking them with a small amount of healthy fat (like olive oil) can improve absorption.
For Vitamin K2: Expand your palate with fermented foods like natto, a traditional Japanese dish made from fermented soybeans, which is an extremely rich source of K2 (MK-7). Other sources include cheeses, eggs, and poultry, which contain other forms of menaquinones.

What About Animal Feed?

It is important to note that menadione's toxicity is dose-dependent and does not apply to all species in the same way. Menadione is widely and safely used as an inexpensive source of vitamin K in regulated amounts for livestock and pet feed, such as for poultry and pigs. This is because these animals can convert the synthetic menadione to menaquinone without the same toxic side effects observed in humans. The difference in metabolism and sensitivity explains this discrepancy. Some manufacturers use the synthetic form in pet food, though this practice is still debated by some experts.

Conclusion

While menadione is chemically related to vitamin K and is sometimes colloquially referred to as vitamin K3, it is not a safe form for human consumption and is banned from dietary supplements. The critical difference lies in its synthetic nature and associated toxicity risks, especially compared to the natural and safe vitamin K1 and K2. The body's own tightly controlled metabolic conversion of K1 to menadione before producing K2 is a natural process that should not be confused with supplementing with synthetic menadione. For optimal health, focus on obtaining natural vitamin K from dietary sources like leafy greens and fermented foods, or through safe, regulated supplements containing K1 or K2.

Sources

National Institutes of Health (NIH) - Health Professional Fact Sheet
Healthline - Vitamin K3 (Menadione)
NCBI - Vitamin K - StatPearls
Wikipedia - Menadione
Pubmed - Menadione is a catabolic product of oral phylloquinone

Frequently Asked Questions

No, menadione is not the same as vitamin K. Menadione is a synthetic (man-made) form, also known as vitamin K3, while the natural forms of the vitamin are phylloquinone (K1) and menaquinones (K2).

Menadione is not used in human supplements because research in the 1980s and 1990s showed it could cause toxicity, including liver damage and the destruction of red blood cells. Its sale for human supplements is therefore banned in countries like the US.

Menadione is a synthetic, water-soluble form of the vitamin, while K1 (phylloquinone) and K2 (menaquinones) are natural and fat-soluble. K1 is found in plants, K2 in fermented foods and animal products, and menadione is man-made and considered toxic for human consumption in supplement form.

Yes, menadione is widely and safely used in regulated quantities as a vitamin K source in feed for livestock and pets. Animals can convert it to an active form of vitamin K without experiencing the same toxic effects seen in humans.

Menadione is chemically synthesized in a laboratory. While it does not occur naturally in foods, the human body does produce it in small, regulated amounts as an intermediate during the metabolic conversion of vitamin K1 to K2.

Vitamin K is essential for blood clotting and bone health. It activates proteins that help blood coagulate and ensures calcium is properly utilized for strong bones and soft tissue health.

To get enough vitamin K safely, you should consume a balanced diet rich in natural sources. Good sources include leafy greens for K1 and fermented foods like natto, eggs, and cheese for K2. Safe K1 or K2 supplements are also widely available.