Magnesium Oxide: Is This Supplement Helping or Hurting You?

Woman suffering from constipation

Story at-a-glance -

  • Magnesium oxide is a common type of magnesium supplement that’s widely available in pharmacies all over the country
  • When taking any type of magnesium supplement, make sure that you follow the recommended dose, and don’t make the mistake of increasing the dosage without informing your doctor, as this may lead to adverse side effects
  • Learn more about magnesium oxide to find out if its benefits outweigh its side effects

Between 50 to 80 percent of the American population is deficient in magnesium. If you’re one of these people, then chances are you’re taking (or planning to take) a form of magnesium supplement.

Magnesium plays a significant role in human health. In fact, researchers have now detected 3,751 magnesium binding sites on human proteins, according to a report by GreenMedInfo.1 This mineral must be bound to another substance to increase its absorption rate, which is why it’s available various forms.2

When searching for the right type of magnesium supplement to take, one of the most common formulations that you may encounter is magnesium oxide. However, medical studies suggest that this form of magnesium does not really deliver the optimum health benefits that you may expect.3

What Is Magnesium Oxide?

Magnesium oxide is a common type of magnesium supplement that’s widely available in pharmacies all over the country. One of the reasons behind its popularity among supplement manufacturers is its low manufacturing cost.4 Nowadays, magnesium oxide is easily and inexpensively obtained through the calcination of naturally occurring minerals.5

Moreover, the magnesium oxide formula contains around 60 percent elemental magnesium — the highest among all types of this mineral supplement.6 This high percentage may lead people into thinking that this type of magnesium supplement is the best of them all. However, just because it has the highest elemental magnesium does not mean that it’s the best form of magnesium supplement that you should take.

Keep in mind that magnesium oxide is non-chelated, which means that it’s not in a form that’s easily absorbed and metabolized by the body.7 Studies have shown that magnesium oxide only has a 4 percent absorption rate, which is relatively poor compared to that of the other magnesium supplements.8

What Are the Sources of Magnesium Oxide?

Magnesium oxide is obtained by burning magnesium in pure oxygen. However, this process is costly, as metallic magnesium is an expensive material. The cheaper way to produce magnesium oxide is by subjecting naturally occurring minerals, particularly magnesium salts, to a process of thermal treatment called calcination.9

There are two magnesium salts that may be used for this process: magnesium carbonate and magnesium hydroxide.10 The possible sources of these magnesium salts are:11


Underground brine deposits

Salt beds

The source of magnesium salt has a great effect on the quality of the calcined material, and this is also the factor that will determine the proper application of the produced magnesium oxide.12 If you’re still considering this supplement, then you should be aware of its other medicinal applications to verify if it’s indeed the right supplement for your needs.

Other Possible Uses of Magnesium Oxide

Aside from increasing magnesium levels, magnesium oxide has also been used to help ease the following conditions:13

Constipation: The low absorption rate of magnesium oxide gives it a strong laxative property, which can induce bowel movement.

Acid reflux: Magnesium oxide acts as an antacid that can help alleviate acid reflux.

Indigestion: Similar to acid reflux, indigestion is also caused by excess acid, which can be neutralized by magnesium oxide.

It’s important to consider magnesium oxide’s laxative property if you’re planning to use it as a supplement because this may cause you to take more trips to the bathroom than usual. If you’re simply taking it to increase the magnesium levels in your body and you’re not really aiming to cure any of the conditions mentioned, then chances are you’ll reach your bowel tolerance long before your body has absorbed a sufficient amount of magnesium.

What’s the Ideal Dosage of Magnesium Oxide?

According to the Food and Nutrition Board, the tolerable upper intake level (UL) for magnesium supplement is 350 milligrams (mg) per day — this dosage is applicable for adults and for children ages 9 years old and above. For kids ages 4 to 8 years old, the recommended UL is 110 mg per day. Moreover, the UL for children between 1 to 3 years old is 65 mg per day.14 However, consult your child’s physician before giving them any type of supplement.

When taking any type of magnesium supplement, make sure that you follow the recommended dose, and don’t make the mistake of increasing the dosage without informing your doctor, as this may lead to adverse side effects.

Side Effects That You May Encounter When Taking Magnesium Oxide

The most common side effects that you may encounter when taking magnesium oxide supplement are abdominal cramping and diarrhea.15 These may be avoided or reduced by eating a meal before taking the supplement. If these symptoms become bothersome, then you should consult your doctor immediately. You should also talk to your doctor if you experience any of these serious side effects:16







Unusual tiredness

Mood swings or mental changes

Considering all the possible side effects that magnesium oxide may cause, it’s really questionable whether the benefits of this supplement really outweigh its risks.

Studies Confirm the Low Efficiency of Magnesium Oxide

There have been a number of studies conducted on magnesium oxide over the past years, and some of these are focused on its bioavailability and solubility.

To give you a background, bioavailability is the actual amount of mineral that’s utilized by your body when you take a particular supplement17 while solubility is the ability of a substance to dissolve in a particular solvent.18 Both of these factors are very important when determining the efficiency of any medicinal drug.

A study conducted by the Center for Mineral Metabolism and Clinical Research compared the solubility of magnesium oxide to another common type of magnesium supplement known as magnesium citrate. The result shows that magnesium oxide is practically insoluble in water whereas magnesium citrate had a high solubility rate.19

Another study also confirmed the poor bioavailability of magnesium oxide compared to the other magnesium supplements available in the market, including magnesium chloride, magnesium lactate and magnesium aspartate.20 The inferior bioavailability and solubility rate of magnesium oxide is the primary reason why it’s not as effective as the other supplements when it comes to optimizing your magnesium levels.

Magnesium Oxide Versus Magnesium Citrate

If you’re looking for a supplement that’s as cheap as magnesium oxide but more effective, then magnesium citrate is something that you may also consider.

Magnesium citrate may have a lower elemental magnesium content compared to magnesium oxide, but its absorption level is still significantly better at 16 percent.21 This means that your body can absorb more magnesium out of this supplement without increasing the recommended amount of intake.

It’s important to note that magnesium citrate may also help alleviate constipation, so it’s not recommended to take if you already have loose bowel movement22 hemorrhoids and/or anal fissures.

Magnesium Threonate: The Magnesium Supplement That I Recommend

Aside from magnesium citrate, another promising magnesium supplement that’s slowly gaining recognition in the market is the magnesium threonate. I personally prefer this magnesium supplement because it has the ability to penetrate the mitochondrial membrane, effectively boosting energy levels. It may also help improve your memory by penetrating the blood-brain barrier.

What’s more, magnesium threonate does not act as a laxative. In fact, it’s formulated for optimum absorption. This makes it an ideal supplement if you want to increase your magnesium levels without affecting your bowel movement.

Natural Alternatives That Help Increase Your Magnesium Levels

Please note that taking a dietary supplement should not be your first option when it comes to improving your body’s magnesium levels. In fact, you can boost your levels through your diet. There’s a variety of  magnesium-rich foods that you can add to your meals, which include:23

Dried agar seaweed

One hundred grams of dried agar seaweed contains 770 mg of magnesium.

Coriander Leaf

Eating 100 grams of dried coriander leaf gives you 694 mg of magnesium.

Rice bran

One tablespoon of rice bran can give you 117 mg of magnesium.

Pumpkin seeds

You can get 156 mg of magnesium by consuming one ounce of pumpkin seeds.

Raw almond

One ounce of soaked roasted almond can give you 80 mg of magnesium. That's 20 percent of the daily value of magnesium that you need.


A half cup of boiled spinach contains 78 mg of magnesium.


One ounce of soaked roasted cashews contains 74 mg of magnesium.


Consider Other Nutrients to Optimize Your Magnesium Levels

Remember that some vitamins may affect the efficiency of a magnesium supplement. If you’re planning to increase your intake of magnesium, then you should increase your calcium, vitamin K2 and vitamin D as well to achieve a balanced nutrient level.

The calcium to magnesium ratio should always be 1:1, since this nutrient can help balance the muscle-relaxing effect of magnesium. The increased intake of calcium may cause arterial calcification, but you can prevent this by increasing your vitamin K2 levels. Vitamin D, on the other hand, helps improve the magnesium and calcium absorption of your body.24,25

Keep in mind that balancing your nutrient levels not only helps you make the most out of your magnesium supplement, but also reduces any possible side effects that it may have.

Frequently Asked Questions About Magnesium Oxide

Q: What is magnesium oxide used for?

A: Magnesium oxide may be used for increasing the magnesium levels in your body. But keep in mind that it's a poor source of magnesium because of its low absorption rate, so it's not really effective when used as a supplement. It is also used by some people as an  antacid and laxative, though,  relieving constipation and stomach discomfort caused by excess acid.26

Q: What is magnesium oxide made of?

A: Magnesium oxide is basically a combination of magnesium and oxygen, but it may also be obtained from magnesium salts, such as magnesium carbonate and magnesium hydroxide.27

Q: Is magnesium oxide acidic?

A: No. Magnesium oxide is a basic oxide with a pH level of 9.28 Acids have a pH level of less than 7.29

Q: How long does it take for magnesium oxide to work?

A: Similar to other magnesium supplements, magnesium oxide takes effect on the body shortly after it's taken. The signs that it's taking effect include diarrhea and abdominal cramping.30 However, if you're using it to increase your magnesium levels, then you should expect it to work slower than the other types of magnesium supplement because of its low absorption rate.31

Q: How much magnesium oxide should I take?

A: The proper dosage of magnesium depends on a lot of factors, including your age, gender and medical conditions. For adults, the ideal upper intake level (UL) for magnesium supplement is 350 mg per day according to the Food and Nutrition Board.32 It's best to consult a doctor to get a prescription that's specifically suited for your needs.

Q: How do I take magnesium oxide?

A: Ideally, you should take magnesium oxide supplement orally with 8 ounces of water. Be sure to take it regularly at the same time each day.33