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Magnesium Oxide: Key Facts, Uses, and How it Works

Magnesium oxide

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Magnesium oxide is a magnesium supplement formed with magnesium and oxygen ions. It’s known as a “magnesium salt,” whereas some other types of magnesium supplements are known as “magnesium chelates.” 

On the chemical level, magnesium oxide consists of a magnesium atom and an oxygen atom, held together through ionic bonding. When water is present, magnesium oxide can become magnesium hydroxide, a related form that is also used as a magnesium supplement. 

Is magnesium oxide the right choice for you? To answer that question, let’s look further into the origins of magnesium oxide, as well as what magnesium oxide is used for today, and then we’ll explore whether magnesium oxide is right for your individual needs (or if you’d do better with a magnesium supplement like Natural Calm).

Magnesium Oxide: A Look Into Its Origins

Magnesium Oxide is also commonly called Magnesia, a name which is derived from the ancient Greek region of the same name.

When the inhabitants of this region located the chalky white substance along the river banks, they called this substance magnesia alba, or “white magnesia.” At the time, magnesium oxide was used for a variety of applications, from usage as a bright white paint to various forms of medicine.

Where does magnesium oxide come from?

While magnesium is the third most abundant element in the Earth’s seawater, and it’s estimated to make up two percent of the crust of the earth as well, magnesium oxide “is mainly produced from the calcination of magnesite in a process similar to the production of lime from limestone. A smaller proportion of the world’s [magnesium oxide] production comes from seawater and brine sources.” It can also be formed via a variety of manual manufacturing processes. (ScienceDirect)

Magnesium oxide has been used in the fields of health and wellness for centuries.

According to research, it “has been widely used as a laxative for many years in East Asia.” These traditional medicinal uses were confirmed over time through clinical studies, and, recently, “the safety, convenience, and low cost of magnesium oxide, which has been used for many years, mean that it has once again attracted attention.”

How Magnesium Oxide Works

In addition to providing a boost to the body’s daily magnesium intake, magnesium oxide works to relieve constipation by drawing water into the solids and allowing them to pass out of the body freely.

Within the acidic stomach environment, the magnesium oxide is converted into magnesium chloride. Then, as a result of pancreatic secretions, it is transformed yet again into sodium hydrogen carbonate by the time it enters the intestinal tract. 

This form of magnesium works to increase “the osmotic pressure of the intestinal lumen fluid, thereby promoting the transfer of water to the intestinal lumen and increasing the water content and volume of the stool. In addition, the swollen stool stimulates the intestinal wall and intestinal propulsive motor activity.” (Magnesium Oxide in Constipation)

In simpler terms, as an osmotic laxative, magnesium oxide draws water in the body into the intestines as it passes through, creating softer bowel movements and helping to restore proper intestinal function.

However, because magnesium oxide is not as bioavailable as other forms of magnesium, more magnesium stays in the intestines, which means more water is drawn in. 

Also, because of how magnesium oxide draws functions as a laxative, it draws water from the surrounding tissues (the intestinal walls). So, it’s important to stay hydrated when taking this form of magnesium. Keeping yourself hydrated in general is just a good idea, but even more so when you’re dealing with constipation. 

The Bioavailability of Magnesium Oxide 

Magnesium oxide is not the most bioavailable form for your body.

Bioavailability simply means the amount of the substance that is taken up in the bloodstream for use in cells. It refers to how effectively something can be absorbed, and put to use by your body. When something has higher bioavailability, your body can more effectively use it. With a lower bioavailability, less of it can be absorbed, and more of it is passed through as waste.

A study conducted by Walker, Marakis, Christie, and Byng compared the relative bioavailability of different forms of magnesium, including magnesium oxide and magnesium citrate (both of which are “magnesium salts”).

The researchers found that, of the magnesium preparations studied, magnesium citrate showed the greatest bioavailability. “We conclude that a daily supplementation with Mg citrate shows superior bioavailability after 60 days of treatment when compared with other treatments studied.” 

When you choose to take any nutritional supplement, it’s important that the supplement be formulated in a way that your body can digest, otherwise the majority of it simply passes through your body and out as waste.  If you are taking a supplement like magnesium oxide to address health concerns and not experiencing the benefits, your body may not be absorbing the magnesium.

However, some forms of magnesium have other primary uses besides simply increasing the magnesium levels in the body.

While magnesium oxide can be taken as a supplement for low magnesium levels, it is more commonly used for digestive complaints such as indigestion and constipation, because less of the magnesium in this form is absorbed by your body, and more remains in your intestines, which increases the laxative effect.

If your goal is to increase your magnesium levels and to get relief from symptoms of magnesium deficiency, it stands to reason that another form of magnesium supplement could be best for you. Magnesium deficiency is a much more common problem than most people realize and could be caused by a lack of magnesium-rich foods in the diet, problems with nutrient absorption, or other chronic health conditions. 

To learn more about magnesium deficiency and what to do about it, check out this comprehensive article on the Natural Calm blog: Magnesium Deficiency: The Complete Guide to Low Magnesium

Is Magnesium Oxide Good for Low Magnesium Levels?

Magnesium oxide as a magnesium supplement is easy to find, but it’s not necessarily the best for long-term usage because of its lower bioavailability. 

As is true for many supplements, magnesium oxide can interact with medications, especially other laxatives, antacids, diuretics, and certain blood thinners. If you experience any reactions (such as rash, hives, itching, dizziness, lightheadedness, weakness, nausea, or vomiting) to taking a magnesium supplement, it’s important to seek medical care right away. 

If you want to boost your low magnesium levels, we recommend that you choose a form that your body is able to process more efficiently and effectively, such as magnesium citrate

How to Take This Type of Magnesium Supplement 

If you choose to take magnesium oxide regardless of the above, let’s discuss the safest way to use this type of magnesium supplement.

Most types of magnesium oxide or magnesium hydroxide supplements come in liquid form. Sold under a variety of brand names, this milky white liquid is often used in the treatment of digestive complaints. 

Magnesium oxide is often used both for laxative effects as well as for magnesium supplementation, because of the stronger laxative effect, more caution should be used when taking it long-term. If you are primarily taking magnesium oxide for magnesium supplementation, follow the dosage information to achieve the best potential result. 

However, if you are reaching for magnesium oxide to resolve your digestive complaints, it’s important to discontinue use if your constipation resolves. Magnesium oxide can be taken in pill or capsule form. Simply follow the instructions on the label or those provided by your pharmacist or medical caregiver. 

When taken in liquid form, it is important to both choose the appropriate magnesium oxide dosage that is correct for your individual needs and also to shake the medicine well before measuring and consuming it. This ensures that the correct dosage is maintained, and none of the materials settle or become imbalanced, which could lead to consuming too much, or too little magnesium oxide for your specific complaint. 

Choose Natural Calm® Magnesium Citrate for Long-Term Wellness


When sorting through all of the different varieties of magnesium supplements available on the market, how do you select the one that’s right for you? 

Award-winning Natural Calm® magnesium citrate offers an easily-absorbable, highly bioavailable magnesium supplement that provides all of the digestive benefits without having to rely on more aggressive, short-term supplement choices. 

Natural Calm® is available in both powder and chewable magnesium gummy form, both of which are delicious and perfect for a busy lifestyle. Taking smaller amounts of magnesium throughout the day means your body can absorb it more effectively, too.

Choose from flavors like raspberry-lemon, watermelon, cherry, orange, or sweet lemon, or try unflavored powder to mix with your favorite drink, as directed. 

Magnesium citrate is a great choice to increase your daily intake of magnesium, provide all of those great digestive benefits and truly nourish the whole body. If you’re not getting enough magnesium from diet (and many of us are not), Natural Calm® might be the best solution for you! 

We’re proud to say that Natural Calm® is still the number one bestselling magnesium supplement in North America and has been for many years. Our products are vegan, non-GMO, and backed by research to take the guesswork out of your magnesium needs.


  • Holappa, Lauri. “Basics of Ferroalloys.” Elsevier EBooks, Jan. 2013, pp. 9–28, Accessed 22 Sept. 2023.
  • Mori, Hideki, et al. “Magnesium Oxide in Constipation.” Nutrients, vol. 13, no. 2, Multidisciplinary Digital Publishing Institute, Jan. 2021, pp. 421–21, Accessed 22 Sept. 2023.
  • AF;Marakis, Walker. “Mg Citrate Found More Bioavailable than Other Mg Preparations in a Randomised, Double-Blind Study.” Magnesium Research, vol. 16, no. 3, Magnes Res, 2022, Accessed 22 Sept. 2023.

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