One of the most widely used additives in drugs and supplements today is magnesium stearate. You’ll actually be hard-pressed to find any supplement sold on the market today that doesn’t include it, though you many not see it named directly. Commonly referred to by other names, such as “vegetable stearate” or derivatives like “steric acid,” it’s virtually everywhere.
In addition to being ubiquitous, magnesium stearate is also one of the most controversial ingredients in the supplement world. In some ways, it’s similar to the vitamin B17 controversy, and there’s debate on whether it’s a poison or a cancer cure. For magnesium stearate, I find this shocking because the detractors don’t have much of a leg to stand on in regard to the peer-reviewed research. Nonetheless, it’s been the focus of a heated debate for decades.
Unfortunately for the general public, natural health experts, supplement companies’ researchers and health care practitioners regularly site conflicting evidence to support their personal opinions — and it’s extremely challenging to get to the facts! If you’ve read some of the reports out there, you know what I mean. Personally, I try to take a practical approach to these types of debates, and I’m always leery of siding with extreme perspectives.
The bottom line is this: Like most fillers and bulk additives, magnesium stearate isn’t healthy in high doses, but it’s definitely not as harmful to consume as some make it out to be because it’s typically only available in minuscule doses.
What Is Magnesium Stearate?
Magnesium stearate is a magnesium salt of stearic acid. Essentially, it’s a compound containing two stearic acids and magnesium. Stearic acid is a saturated fatty acid found in many foods, including animal and vegetable fats and oils. Cocoa and flaxseeds are examples of foods that contain substantial amounts of stearic acid. (1, 2)
After magnesium stearate is broken back down into its component parts in the body, its fat is essentially the same as that of stearic acid. Some sources even claim that the magnesium part of it can be used to supply the body with this essential mineral. (3) Considering the widespread prevalence of magnesium deficiency, this suggests that magnesium stearate can actually have a beneficial effect on the body.
The Purpose of Magnesium Stearate
Magnesium stearate is the most common ingredient used in forming tablets because it’s a fabulous lubricant. Known as a “flow agent,” it helps speed up the manufacturing process because it prevents ingredients from sticking to the mechanical equipment. Just a miniscule amount is required to coat a powder blend of virtually any drug or supplement mixture.
Not only is it fantastic for manufacturing purposes because it allows for smooth transport on the machines that produce them, but it makes the pill easier to swallow and move down the gastrointestinal tract. Magnesium stearate is also a common excipient, which means it helps enhance the therapeutic effect of the active ingredient of various medications to promote drug absorption and solubility. Known as safe vehicles for drugs, excipients also help give pills a uniform consistency.
Some claim that it’s possible to produce a drug or supplement without excipients like magnesium stearate, which begs the question why they’re used when more natural alternatives are available. But that may not be the case. In the words of the largely popular NOW Foods company:
NOW is reformulating some products with alternatives to mag stearate, using such natural excipients as ascorbyl palmitate, but we’re doing it where it makes sense and not because we misunderstand the science. These alternatives don’t always work, though, having different physical properties. (4)
At this point, it’s still unclear whether magnesium stearate alternatives are probable or even needed.
Magnesium Stearate’s Potential Side Effects
NOW is quite confident that magnesium is non-toxic. Its website states that:
Just like other chelated minerals (magnesium ascorbate, magnesium citrate, et al), [it] has no inherent negatives based on its being in a stable neutral compound comprised of a mineral and a food acid (vegetable sourced stearic acid neutralized with magnesium salts). (5)
On the other hand, in its report on magnesium stearate, the National Institute of Health (NIH) poses the threat of magnesium overdose in impairing neuromuscular transmission, and that it can cause weakness and diminished reflexes. Although extremely rare, the NIH reports that:
Thousands of exposures occur every year, but severe manifestations are very rare. Severe toxicity is most common after intravenous infusion over multiple hours (usually for pre-eclampsia), and can occur after chronic excessive doses, especially in the setting of renal insufficiency. Severe toxicity has been reported after acute ingestion but is very rare. (6)
Nonetheless, this report hasn’t put everyone’s mind to rest. Just a quick glance at Google, and you’ll find magnesium stearate connected to a number of side effects, such as:
Poor Intestinal Absorption
Because it’s hydrophobic (“water loving”), there are reports suggesting that magnesium stearate can slow down the rate at which drugs and supplements are dissolved in the gastrointestinal tract. (7) Directly affecting the ability of the body to absorb chemicals and nutrients, the protective nature of magnesium stearate can theoretically make a drug or supplement veritably useless if the body can’t break it down properly.
On the flip side, a study conducted at the University of Maryland claims that magnesium stearate didn’t affect the amount of chemicals that were released from propranolol hydrochloride (a drug used to control rapid heart rate and bronchospasm), so the jury is still out on this one. (8)
Suppressed T Cells
A key component of your body’s immune system to attack pathogens, T cells are affected not by magnesium stearate directly, but by steric acid (the main component of the common bulking agent). The landmark study first describing this was published in the journal Immunology in 1990, which uncovered how T-dependent immune responses were inhibited in the presence of steric acid. (9)
In a Japanese study evaluating common excipients, vegetable magnesium stearate was actually discovered to be a formaldehyde-causing agent! (10) This may not be as scary as it sounds, though, as formaldehyde is naturally found in many fresh fruits, vegetables and animal products. (11)
To help put your mind to rest, magnesium stearate produced the least amount of formaldehyde out of the entire selection of excipients tested at 0.3 nanograms per gram of magnesium stearate. To put this into proper perspective, eating a dried shitake mushroom produces upward of 406 milligrams of formaldehyde per kiligram consumed! (12)
In 2011, the World Health Organization published a report outlining how several batches of magnesium stearate became contaminated with potentially harmful chemicals, including bisphenol A, calcium hydroxide, dibenzoylmethane, Irganox 1010 and zeolite (sodium aluminium silicate). Because it was an isolated incident, we can’t jump to premature conclusions that people who take supplements and prescription drugs with magnesium stearate should be concerned with toxic contamination.
Before you boycott all of your supplements and natural health foods that include it as a bulking agent or filler, it’s important to think in terms of “dose dependency.” In other words, next to intravenous overdose for severe medical conditions, magnesium stearate has only been shown to be harmful in laboratory studies where rats were force-fed such as exorbitant amount that no human on the planet could ever consume that much.
Case in point, in 1980 the journal Toxicology described the results of a study that took 40 rats and fed them a diet of either 0 percent, 5 percent, 10 percent or 20 percent magnesium stearate in a semisynthetic diet for three months. Here’s what it found: (13)
- 20% group: Decreased weight gain, reduced liver weight, increased amount of iron, kidney stones and nephrocalcinosis (a condition where too much calcium is deposited in the kidneys, which has been linked to premature babies).
- 10% group: Reduced liver weight.
- 0% – 5% group: No side effects observed, which corresponds to less than 2500 milligrams per kilogram of body weight per day.
As explained by Gene Bruno, MS, MHS:
It should be noted that the amounts of stearic acid and magnesium stearate typically used in a tablet is relatively minute. Stearic acid typically ranges between 0.5 [percent]–10 percent of the tablet weight, while magnesium stearate typically represents 0.25 [percent]–1.5 percent of the tablet weight. Therefore, in a 500 milligram tablet, the amount of stearic acid would probably be about 25 milligrams, and magnesium stearate about 5 milligrams. (14)
Too much of anything can be harmful, and people can die from drinking too much water, right? This is important to keep in mind because for someone to be harmed by magnesium stearate, that person would need to consume literally thousands of capsules/tablets in one day!
The Bottom Line
Truth is, magnesium stearate and all of its derivatives are cost-effective additives for pharmaceutical and supplement manufactures. Yet, at the same time, they pose little-to-no threat to people who consume them as a part of their natural health supplement regimens. All of the reports out there claiming that the bulking agent will cause harm are simply not founded on science.