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Toxicity of Magnesium Stearate

Magnesium stearate is a compound with the chemical formula Mg (C18H35O2)2. It's one of a class of drug additives called excipients, inactive compounds that help bind the active ingredients in the drug together or fill up a capsule when the active ingredient wouldn't be enough to take up all the space in the capsule by itself. While some Internet rumors suggest that magnesium stearate is unsafe, it is generally believed--based on the available evidence in 2010--that magnesium stearate as a food and drug additive does not pose any threat to human health.

  1. Manufacture

    • Many of the fat molecules in your body and in other animals are triglycerides--three long chains of hydrocarbons called fatty acids attached to a single molecule of glycerol. Stearic acid is a fatty acid that's especially common in animal fats, although it's also found in cocoa butter as well. Treating animal fats with hot water under pressure can split the triglycerides to release the stearic acid. Magnesium stearate is a combination of stearic acid and magnesium, usually obtained through a process involving several other intermediate reactions.

    Composition and Properties

    • A stearate is basically a stearic acid that has lost a hydrogen ion so that it has a net negative charge. Magnesium stearate is a combination of two stearates with a magnesium ion. At room temperature magnesium stearate is a white powder with a melting point of 88-90 degrees Celsius.

    FDA Evaluation

    • The FDA considers magnesium stearate to be a substance "generally recognized as safe." In a 1979 review, the FDA noted that, "None of the available evidence suggests any probable hazard when any of the GRAS compounds of magnesium is used as a food ingredient." While there have been rare incidents reported where large quantities of magnesium stearate caused an adverse reaction, the amounts ingested in these cases were "orders of magnitude greater than the daily intake of magnesium added to food." The FDA does not believe that magnesium stearate poses any serious threat to human health.

    Dietary Sources

    • Magnesium is actually one of the most common minerals in the body and is vital for certain biochemical processes. It's considered an essential nutrient in the diet and is especially plentiful in foods like fish, nuts, spinach and soybeans. Stearic acid is likewise very common in beef fat, cocoa butter, shea butter and various other foods.

    Possible Hazards

    • None of the available evidence suggests that magnesium stearate poses any threats to human health at the levels found in prescription drugs and dietary supplements. Magnesium stearate may slow the release of a drug, but the amount of the drug ultimately absorbed into your bloodstream will be the same. Magnesium stearate is chemically stable, but can react with strong oxidizing agents like those found in bleach, so it's best not to mix it with bleach or other similar chemicals.

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