What Is Magnesium Stearate?

Medically Reviewed by Poonam Sachdev on June 23, 2021

Magnesium stearate is a salt that forms when stearate molecules bond with a magnesium ion. Stearate comes from stearic acid, a long-chain saturated fat found in:

  • Beef
  • Chicken
  • ‌‌Cocoa butter
  • Coconut oil
  • Eggs
  • Milk and dairy products
  • Palm oil
  • ‌Salmon

Experts say stearic acid is the only long-chain saturated fat that does not raise cholesterol levels.

In the form of a powder, the salt forms the coating that you see on medications and vitamins.  Magnesium stearate may stick to your hands and feel greasy when you touch it. Makers of many processed foods, cosmetics, and pharmaceuticals also add magnesium stearate to their products. 

What Is the Purpose of Magnesium Stearate?

Medications. Companies call magnesium stearate a “flow agent.” Its main job is to keep the ingredients in a capsule from sticking together. It also forms a barrier between the medicines and the machines that make them. The powder improves the consistency and quality of the medication capsules.

Another function of the powder is to slow the absorption and breakdown of drugs. This way, your body absorbs them in the correct area of your bowel. Without magnesium stearate, it would be hard to predict a medication's outcome, quality, and consistency.

Cosmetics. In the cosmetic world, magnesium stearate is a helpful ingredient for many things. It acts as a bulking agent, an anti-caking agent, a colorant, and more. Here, it is a low-hazard product, but data on this is limited.

The Health Effects of Magnesium Stearate

Magnesium stearate is generally safe to consume, but too much of it can have a laxative effect. In large amounts, it can irritate the mucus lining of the bowels. This may trigger a bowel movement or diarrhea.

Immune function. The powder may weaken your immune T-cell function. Studies on this effect are still in the early stages.

Pesticide concerns. Stearate sometimes comes from cottonseed oil. Some people worry that it may have pesticides that can be dangerous when consumed. Magnesium stearate goes through an intense purification process before being used in medications.

Another concern is that cottonseed oil is genetically modified. But the chemical structure of stearic acid remains the same regardless of its source. 

Nutrients and drug absorption. There is some concern that magnesium stearate might keep the body from absorbing nutrients the way it should. One study found that tablets with magnesium stearate take longer to dissolve than those without. 

Other research found that how long magnesium stearate takes to dissolve has no effect on a drug's effectiveness. It also doesn't change the dissolution of the tablet or the potency of the supplement or drug.

Biofilms. There are also concerns that magnesium stearate can cause the formation of harmful biofilms in the digestive system. Biofilms happen when groups of bacteria form a protective barrier. These claims come from the fact that soap has magnesium stearate and makes a scum film. But your intestinal lining is different from your bathroom walls or doors and won't have the same scum film.

Allergens. Allergic reactions to magnesium stearate are rare, but you should avoid it and talk to your doctor if it affects you.

How Much Magnesium Stearate Is Safe to Consume?

The FDA has approved magnesium stearate as a safe product and allows its use as an additive in foods and supplements.

The National Center for Biotechnology Information (NCBI) also says it is safe for use in small quantities. It recommends fewer than 2,500 milligrams (mg) per kilogram daily. This equals about 170,000 mg for a 150-pound adult, much more than what you’d take in supplements. 

Show Sources


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Frontiers for Young Minds: “Big bad Biofilms: How Communities of Bacteria cause Long-Term Infections.”

Healthy Eating Club: “Saturated fats.”

International Journal of Pharmaceutics: “Delay effect of magnesium stearate on tablet dissolution in acidic medium.”

National Center for Biotechnology Information: “Delay effect of magnesium stearate on tablet dissolution in acidic medium.”, “Magnesium stearate.”, Magnesium stearate, a widely-used food additive, exhibits a lack of in vitro and in vivo genotoxic potential.”, “Molecular basis for the immunosuppressive action of stearic acid on T cells.”

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Research Gate: “Magnesium stearate, a widely-Used food additive, exhibits a lack of in vitro and in vivo genotoxic potential.”

The Vegetarian Resource Group: “Magnesium Stearate.”

Thomas Buttke and Paul Tebbey: “Molecular basis for the immunosuppressive action of stearic acid on T cells.”

U.S. Food & Drug Administration: “CFR-Code of Federal Regulations Title 21.”

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