Magnesium stearate is an almost universal ingredient in tablets and capsules. This remarkably controversial additive has many claims against it. What are they based on? Are any of them true? Read on to learn if supplements without magnesium stearate are actually safer.
What Is Magnesium Stearate?
Magnesium stearate is a common inactive ingredient in supplements and medications. In fact, it’s almost universal – but why? What does it do ?
In brief, magnesium stearate – also called magnesium octadecanoate – is a filler. It has no pharmaceutical function; instead, it is used to change the texture of foods and to press supplements and medications into tablets and capsules. It is one of the most common additives in the pharmaceutical industry because it is considered very safe to consume [1, 2].
Despite its widespread usage and excellent safety profile, magnesium stearate has become a controversial topic in the last decade or so. Claims circulate online that it is a toxic chemical that will line your intestines like soap scum or trigger spontaneous arthritis.
So what’s the truth?
Stearic acid is a type of fat molecule found in almost all fats – animal and vegetable. For example, beef fat, cocoa butter, shea oil, and sal oil are all very high in stearic acid. In a western diet, beef and chocolate are the biggest sources of stearic acid day to day .
Stearic acid is a saturated fat. Most saturated fats raise LDL (bad) cholesterol, so one might think stearic acid is unhealthy. However, stearic acid appears to have no effect on LDL cholesterol on its own – and when it replaces trans fats in a person’s diet, it may actually lower LDL cholesterol [5, 6].
Vegetable Magnesium Stearate
Some supplements specify that the magnesium stearate in the product is from a vegetable source. Sometimes, it is listed as vegetable magnesium stearate or even just vegetable stearate.
Functionally, magnesium stearate from beef fat and from vegetable fat are very similar. Only people who maintain strict vegan/vegetarian diets or who have alpha-gal allergies need to be concerned about the difference [7, 8].
- Very safe and easy to digest
- Few reported side effects in the scientific literature
- May trigger anaphylactic reactions in people with alpha-gal allergies
- A very rare allergy may cause rashes
Magnesium Stearate Uses
Magnesium stearate is used as a lubricant and anti-adherent in supplements and medications. It’s a little bit greasy, so it stops supplement or medication powders from clumping up and sticking to the mixing and pressing machinery [1, 9].
When magnesium stearate is added, it keeps everything flowing smoothly and mixing evenly. This is how pharmaceutical and health food companies make sure that each tablet or capsule is exactly the same, without variations in the number of active ingredients [1, 9].
Magnesium stearate also keeps tablets from getting stuck in the press during manufacturing. Once packaged, magnesium stearate holds the tablets in their shape and resists breakage .
How it Works in Your Body
During digestion, magnesium stearate dissolves into its component parts: magnesium and stearic acid. Magnesium is an essential mineral and stearic acid is a highly digestible fat found in many foods [1, 5].
Magnesium Stearate Side Effects, Safety & Common Concerns
Magnesium and stearic acid are highly digestible and even beneficial. Researchers have also conducted multiple studies to check for any unexpected toxicity, and they’ve found nothing. You would have to consume around 5 g of magnesium per day to expect any symptoms of magnesium toxicity, for example [1, 12].
So, if magnesium and stearic acid are so safe and easily digestible, why are we talking about it? What is the controversy? Do the naysayers have a leg to stand on?
It’s not clear exactly when or where the magnesium stearate controversy began. A handful of articles from health, fitness, and dieting websites warn of mysterious side effects and contamination with toxic chemicals. Most of these articles either do not provide evidence or cite sources that contradict their conclusions.
Many more articles confirm the safety of magnesium stearate as an additive, but their comments sections are full of people claiming that this compound caused allergic reactions or arthritic pain.
People online have reported all kinds of anecdotal side effects and potential harms of magnesium stearate. Let’s discuss a few of the most common and whether magnesium stearate may be the culprit.
According to all toxicology studies so far, magnesium stearate absolutely does not cause bothersome side effects in the average person at the dosages encountered in supplements and medication.
In a rat study, animals that ate magnesium stearate at 10 – 20% of their diets experienced side effects like reduced liver weight and kidney disease. At 5% of the diet, equivalent to about 2,500 mg per kg of body weight per day, the rats had no side effects at all .
Tablets and capsules typically contain around 1% magnesium stearate – only a couple of milligrams per pill. In other words, the average person would have to take tens of thousands of pills per day to consume a harmful quantity of magnesium stearate [13, 14].
Impurities and Contaminants
Some articles have claimed that magnesium stearate is frequently contaminated with other chemicals, and that these chemicals cause unwanted side effects. They occasionally base this claim on a 2011 WHO report of contamination in a batch of magnesium stearate.
This report confirms that one batch of magnesium stearate manufactured in Ohio contained zeolite, calcium hydroxide, dibenzoylmethane, bisphenol A (BPA), and Irganox 1010. However, the report concluded that these contaminants were present in such tiny amounts that they did not pose a health risk .
Besides this single report, it’s worth noting that fillers labeled “magnesium stearate” often contain palmitic acid as well as stearic acid. Palmitic acid is another easily digestible fatty acid that is commonly found in many foods. Palmitic acid is more likely to raise cholesterol and contribute to heart disease than stearic acid, but it is not toxic [1, 16].
Some articles claim that magnesium stearate can form a film on the inside of the intestines, preventing the gut from absorbing medicine and nutrients.
Where does this claim come from? There are a couple of possibilities. First, magnesium stearate does form films on and around other filler ingredients. It can also be used to make environmentally friendly, biodegradable “plastic” films. Finally, magnesium stearate is one of the molecules that makes films of soap scum in bathtubs and showers [14, 17, 18].
Fortunately, we can be very confident that these cases do not apply to the insides of our bodies: magnesium stearate dissolves into magnesium and stearic acid in the intestines, and both of these are easily absorbed and metabolized .
Some people have claimed that magnesium stearate actually prevents active compounds from dissolving and being absorbed efficiently in the intestine. This one’s tricky, because it’s technically true but not something we, the consumers, have to worry about.
Magnesium stearate makes up a very small proportion of a tablet of medication, and even small variations in the formula can change how quickly the tablet dissolves. In one study, tablets with 0.77% magnesium stearate dissolved significantly faster than those with 1.1% magnesium stearate. It was enough of a difference to affect drug release .
However, this type of study is not about whether existing supplements and medications can be absorbed correctly. These studies help pharmaceutical companies determine how much magnesium stearate they can or should add to a tablet formula before the tablets go to market .
Active compounds delivered in solid tablets are not absorbed as efficiently as liquid gel caplets or tinctures. However, the difference between absorbing solids and liquids and has little to do with magnesium stearate .
Some articles claim that magnesium stearate kills your T cells and weakens the immune response. This claim seems to be based on a single study wherein T cells from mice were exposed directly to a bath of stearic acid, and the T cells subsequently died .
There are two glaring problems with using this study to claim that magnesium stearate is toxic. First: the study used stearic acid, not magnesium stearate. Second: your T cells will never be exposed to stearic acid in as high a concentration as was used in this study .
On top of that, this study used T cells from mice, not humans. Human T cells and mouse T cells differ in how they break down fat, and stearic acid would not affect human T cells the same way .
Here’s a very strange case that doesn’t come up in most health articles, but occasionally appears in reader comment sections.
When a person is bitten repeatedly by the lone star, brown dog, or Australian paralysis ticks, that person is at risk of developing a very rare condition called alpha-gal allergy, or simply alpha-gal. People with this allergy cannot eat or sometimes even touch anything containing galactose-alpha-1,3-galactose (hence, alpha-gal) .
The trouble is that alpha-gal is in just about every product that comes from a non-primate mammal. That includes beef, pork, and lamb meat. The allergy is severe, often producing a delayed anaphylactic reaction two or more hours after the person has eaten red meat .
People with alpha-gal claim to have allergic reactions to tablets containing magnesium stearate, and they appear to have a leg to stand on. There has been at least one confirmed case of alpha-gal allergy producing a reaction to beef-sourced magnesium stearate [8, 23].
People with alpha-gal should avoid magnesium stearate. Vegetable sourced magnesium stearate should be okay, but when in doubt, stay on the safe side.
Allergies and Hypersensitivity
Some people who don’t have alpha-gal claim to have allergic reactions to magnesium stearate. This is technically possible, but very rare. At least one case study has presented a young woman with an allergy to magnesium stearate that caused a rash to break out on her skin. In veterinary practice, one case study has proposed a magnesium stearate skin allergy in a dog [24, 25].
So it looks like magnesium stearate allergies exist, but they are extremely rare.
What About Drug Interactions?
Some drugs are considered incompatible with magnesium stearate. These include :
- Oxprenolol hydrochloride
- Fosinopril sodium
- Doxylamine succinate
These drugs, as well as several others, react with magnesium stearate over time. If magnesium stearate were added to tablets or capsules of these drugs, some portion of the drug would react and be converted into a different compound. This reaction would make the drug less effective .
Even if you take these medications, you probably don’t need to worry about them interacting with magnesium stearate. These reactions often take between two and four weeks in the intact pills, at room temperature; they wouldn’t have enough time to make a difference during transit through the small intestine, which generally lasts less than five hours [26, 27].
Supplements without Magnesium Stearate
If you still want to avoid magnesium stearate, you have options!
Some tablets and capsules use alternative additives like sucrose fatty acid esters and glyceryl monostearate. As the names suggest, however, some of these compounds also include stearic acid [28, 29].
To avoid fatty acid-based additives entirely, choose supplements (and, when possible, medications) in forms other than tablets. Many supplements are available as raw herbs, liquid extracts or tinctures, gummies, jellies, or gel capsules.
Magnesium stearate is a safe and digestible additive in supplements and medications. Your body breaks it down to magnesium and stearic acid, both of which are easily absorbed and removed. If you’re vegan/vegetarian, vegetable magnesium stearate is simple to find.
Allergies to magnesium stearate are possible, but very rare.
The claims about its side effects and contamination with toxic chemicals are largely unfounded. Still, if you’re worried, you can avoid magnesium stearate by looking for raw herbs, liquid extracts or tinctures, gummies, jellies, or gel caps.