Claim your FREE Report: 15 Steps to Raising the Healthiest Pet You Know!

Magnesium Stearate: Harmful for Your Dog or Cat?

The Internet can be a wonderful place to research your most burning questions, but it can also cause a ton of confusion and is known to share some misleading and downright false information. For that reason, one of the things I like to do is peruse the Internet for “information” that my clients and readers may come across and then to provide the facts if I feel that any of this information may be distorted, misleading or sometimes even false. The reason I feel this is important is because we all want the best for our companion animals, and we don’t need more stress caused by people telling us – erroneously – that something we are doing or not doing is harming them if in fact this is not the case. That’s why I want to set the record straight regarding magnesium stearate.

magnesium stearate capsules

Recently, I have been coming across a lot of statements about the dangers of magnesium stearate, which is an ingredient that is found in some of the most high-end supplements and is quickly becoming a topic of debate. Many supplement companies, as well as healthcare professionals, are sharing what appears to be “evidence”, sometimes because they mean well and sometimes, I suspect, to support their own products or personal opinions. This can make things very confusing for the consumer.

Before you read any more alarming “facts” about magnesium stearate, I want to present the real facts – and the scientific evidence – to help you make an informed decision the next time you are shopping for a product containing this ingredient for your four-legged pal.

What is Magnesium Stearate?

Magnesium stearate is a compound salt of magnesium and stearic acid. Magnesium is an essential mineral and is certainly not harmful. Stearic acid is a long-chain saturated fatty acid found in many common foods, including beef, eggs and coconut oil, cheese, salmon and even human breast milk – just to name a few.[1] According to scientists, stearic acid is the only long-chain saturated fat that doesn’t increase cholesterol or contribute to the risk of heart disease.[2]

Magnesium stearate is a desirable additive in many supplements because it serves as a “flow agent.” This means that it prevents ingredients from sticking to each other and to the manufacturing equipment. In this manner, it helps the ingredients in the capsule homogeneously blend together at a proper and consistent dose and remain at the same level from capsule to capsule.[1][2]

The Myth’s Behind Magnesium Stearate

Now that you know what it is, let’s talk about the myths surrounding magnesium stearate:

Magnesium Stearate is Toxic

One of the most commonly talked about myths is the idea that magnesium stearate is toxic. However, is that really true? After putting on my detective gloves, I am here to tell you that there is no evidence that magnesium stearate is toxic – or even close – at levels contained in supplements.

Let’s put some things into perspective. First of all, as we mentioned, stearic acid is found in many foods. So much so, in fact, that a US adult consumes an average of about 7,000 mg per day of stearic acid from food. To put this in perspective, if you took 20 vitamin capsules weighing 500 mg each and containing 1% magnesium stearate, you would consume less than 96 mg of stearic acid per day. (Manufacturers typically use 0.25% – 5% magnesium stearate in nutritional formulations).[1]

The safe level of magnesium stearate for humans is considered to be anything below 2,500 mg/kg of body weight per day, which equates to just more than 170,000 mg per day for a 150-pound adult.[1] To put this in “dog speak,” it also equates to more than 45,000 mg per day for a 40-pound dog!

Magnesium Stearate Prevents Drug Absorption

This is a dubious claim at best. One study showing that magnesium stearate increased the time it took for a drug tablet to dissolve was conducted in vitro (in a test tube) using artificial gastric juices.[3] However, a different study showed no difference in tablet dissolution time.[4] Yet another study showed that there was no change in bioavailability of drugs containing magnesium stearate, even in the instance when the time to dissolve increased.[5]

Magnesium Stearate Immunosuppresses T-cell Function and Causes the Collapse of Membrane Integrity

This is one of the most misleading myths about this ingredient, and it’s important to know that there is only one study in question when it comes to magnesium stearate in regards to T-cell function. The study in question was conducted on mice, not humans, and certainly not dogs. This is a very important distinction, and I will tell you why in a moment.

This study was done in 1990, using mouse T-cells in a Petri dish. During this study, when mouse cells were excessively incubated with stearic acid (not magnesium stearate,) the study showed a collapse of the cell membrane and a loss of T-cell function. The conclusion: Mouse T-cells can collapse with high levels of stearic acid.[6]

First of all, as I just mentioned, this study used stearic acid, not magnesium stearate. Yes, the same stearic acid that I earlier states is contained in many common foods.

Secondly, and of critical importance, is that mice lack the enzyme known as delta 9-desaturase, which de-saturates fatty acids and in this instance synthesizes the saturated fatty acid stearic acid into the healthy mono-unsaturated fatty acid oleic acid. To give you some perspective, olive oil is one of the richest sources of oleic acid.

Like people, dogs do have the delta-9 denatures enzyme, enabling them to de-saturate stearic acid into oleic acid. Therefore, this study on mice is completely irrelevant to dogs and people.

Magnesium Stearate is Genetically Modified and Chock Full of Pesticides

As many of you know, I am greatly concerned about and have written extensively on GMO’s. The stearic acid used for magnesium stearate is most often derived from cottonseed oil, which is often genetically modified. However (and this is an important point), stearic acid contains a specific chemical structure that remains unchanged regardless of the source – be it from a genetically modified cotton plant or from human breast milk. Therefore, where the crude fat in the product comes from should not at all effect the final form of the stearate.[2]

Many people also believe that magnesium stearate is heavily contaminated with pesticides because it comes from cottonseed oil. However (and, again, this is another important point), the magnesium stearate found in supplements is highly purified via a refining process.[2]

Magnesium Stearate Affects the Intestinal Biofilm

This is really a great example of Internet information gone-awry. Around the Internet, people state that magnesium stearate can cause harmful biofilms to form in the intestine. As nutritional expert Chris Kresser puts it: “This assertion appears to be based on the fact that soap scum contains magnesium and calcium stearate, so they insist that just as soap scum creates films on your sink or shower, magnesium stearate creates films on your intestines. It should be pretty obvious that the intestinal lumen is a vastly different environment from a shower door, but some people still seem to be concerned. Rest assured, there is no conceivable reason why this would take place, and I haven’t seen a single scientific article that even hints at this possibility.”[2]

My Conclusion

After reading research studies and putting on my own investigation hat, I strongly feel that in normal levels contained in supplements your dog or cat may take, that magnesium stearate is safe. All the reports out there claiming that this ingredient causes any harm are simply not founded on science.

Oh, and please note that I am not suggesting that you dump magnesium stearate into your dog or cat’s food! I am simply providing you with the scientific evidence surrounding this ingredient’s use in supplements, so that you can objectively evaluate false claims and scare-mongering running rampant on the Internet.

Do you have something to add to this story? Voice your thoughts in the comments below!
Are you on social media? Let’s connect!
Facebook | Google+ | RSS | Twitter | YouTube

  1. [1]English, J. (2013). Magnesium Stearate: A Safe and Effective Filler – Setting the Record Straight, Nutrition Review, Retrieved from
  2. [2]Kresser C. (2013). Harmful or Harmless: Magnesium Stearate, Retrieved from
  3. [3]Uzunović A & Vranić E. (2007). “Effect of Magnesium Stearate Concentration on Dissolution Properties of Ranitidine Hydrochloride Coated Tablets”, Bosnian Journal of Basic Medical Sciences, vol. 7, no. 3, pp. 279-283. Retrieved from
  4. [4]Eddington ND, Ashraf M, Augsburger LL, Leslie JL, Fossler MJ, Lesko LJ, Shah VP & Singh Rekhi G. (1998). “Identification of Formulation and Manufacturing Variables that Influence In Vitro Dissolution and In Vivo Bioavailability of Propranolol Hydrochloride Tablets”, Pharmaceutical Development and Technology, vol. 3 no. 4, pp. 535-547.
  5. [5]Singh Rekhi G, Eddington ND, Fossler MJ, Schwartz P, Lesko LJ & Augsburger LL. (1997). “Evaluation of in Vitro Release Rate and in Vivo Absorption Characteristics of Four Metoprolol Tartrate Immediate-Release Tablet Formulations”, Pharmaceutical Development and Technology, vol. 2, no. 1., pp. 11 – 24.
  6. [6]Tebbey PW & Buttke TM. (1990, July). “Molecular Basis for the Immunosuppressive Action of Stearic Acid on T Cells”, Immunology, vol. 70, no. 3, pp. 379-384. PMID: 2379942.


  1. Elizabeth says:

    It also has aluminum in it ! My aluminum levels were up and it was traced back to my magnesium..

    • Hi Elizabeth,
      Thank you for your comment. I would be interested to know how it was traced back to your magnesium and specifically to magnesium stearate. There is nothing inherent in magnesium stearate that contains any aluminum. Several years ago, a manufacturer of magnesium stearate had an issue with contamination and zeolite (sodium aluminum silicate) was one of the problems. However, this was an isolated incident and can happen with ANY ingredient. It has nothing specifically to do with magnesium stearate, but rather points to the crucial need to buy supplements from reputable manufacturers that perform strict tests for contamination and purity.