Magnesium Oxide: Benefits, Side Effects, Dosage, and Interactions

Magnesium oxide is an inorganic salt of magnesium formed with ions of magnesium and oxygen (2).

It’s one of many forms of magnesium available for purchase in supplement form. It’s added to dietary supplements as well as over-the-counter medications used to treat constipation, indigestion, and headaches.

Compared with other forms of magnesium, it may be less effective at raising blood magnesium levels (3).

How does it compare with other forms of magnesium?

Magnesium oxide and other inorganic salts of magnesium like magnesium carbonate are high in elemental magnesium, which is the total amount of magnesium in a supplement (3).

However, they have a low solubility rate, making them less bioavailable than other forms of the mineral. So, even though magnesium oxide supplements provide a good amount of magnesium, it’s not the most available form for your body to utilize (3).

A 2019 study confirmed this by testing 15 magnesium supplements and finding that a supplement containing only magnesium oxide had the lowest bioavailability (3).

Meanwhile, a supplement with both inorganic and organic magnesium salts — magnesium oxide and magnesium glycerophosphate, respectively — had the highest bioavailability (3).

Because of its low absorption rate in your intestines, magnesium oxide may lead to digestive effects like diarrhea. In fact, its strong laxative effects are why it’s commonly used to treat constipation (3).

A 2017 rat study demonstrated its low absorption rate, concluding that only 15% of orally administered magnesium oxide was absorbed, while 85% was excreted in the feces. Older research suggests the absorption rate is even lower in humans (4, 5).

In contrast, magnesium citrate, magnesium acetyl taurate, magnesium malate, and magnesium glycinate all have high absorption rates and are more effective at increasing magnesium levels in the body (6, 7, 8, 9, 10).

Still, magnesium oxide has been shown to offer several benefits and is commonly used to treat medical conditions like chronic constipation.

Summary

Magnesium oxide is an inorganic salt of magnesium. Even though it contains high amounts of magnesium, it has low absorbability in the body. Still, it has been shown to offer health benefits like constipation relief.

Research shows that magnesium oxide is effective at treating certain medical conditions.

May help treat headaches

Magnesium is needed for proper nerve cell functioning. As such, a deficiency in this mineral can lead to migraine headaches.

Studies show that magnesium oxide may reduce headache symptoms. It may even be as effective as some migraine headache medications (11).

For example, a 2021 randomized, controlled, double-blind study in 63 people who experienced migraine found that taking 500 mg of magnesium oxide daily reduced migraine frequency as effectively as a migraine medication called valproate sodium (12).

Older research also suggests that magnesium oxide may reduce migraine in children (13).

However, other forms of magnesium like magnesium sulfate and magnesium citrate may be more effective at treating migraine, as they are typically better absorbed (14, 15, 16).

May reduce stress and anxiety

Magnesium plays an important role in your body’s stress response. In fact, studies have shown that people who experience frequent stress tend to have lower magnesium stores (17).

Some studies have shown that supplementing with magnesium may help reduce levels of stress and anxiety in certain populations.

For example, a 2017 review of 18 studies found that magnesium oxide may reduce stress and anxiety in women with premenstrual syndrome, but only when combined with vitamin B6 (18).

Despite these promising results, researchers acknowledge that the quality of existing studies on the subject is poor, and future well-designed studies are needed (18).

Helps treat constipation

One of the most common uses of magnesium oxide supplements is constipation treatment. The supplement has an osmotic effect, meaning it draws water into the intestines to cause a laxative effect that can help relieve constipation in both children and adults.

In a small 2019 randomized, double-blind, controlled study, 34 women with mild to moderate constipation were treated with either 1.5 grams of magnesium oxide or a placebo daily for 4 weeks (19).

Many women in the magnesium group experienced significantly improved bowel movement frequency, stool form, colonic transport time, and quality of life compared with the placebo group (19).

In fact, over 70% of those treated with magnesium oxide reported overall symptom improvement, compared with only 25% of those in the placebo group (19).

Similarly, a study in 90 people with constipation found that taking either 1.5 grams of magnesium oxide or 1 gram of senna, another laxative, significantly improved spontaneous bowel movements and constipation-related quality of life compared with a placebo (20).

Magnesium oxide has also been shown to prevent constipation after surgery, treat opioid-induced constipation, and improve functional constipation in children (21).

That said, while magnesium oxide has been shown to be safe for treating constipation, it may lead to dangerously high magnesium levels in certain populations, such as those with kidney impairment and older adults (5).

May lower blood pressure

Magnesium oxide supplements may help reduce elevated blood pressure levels.

A 2018 study in 48 people with high blood pressure found that treatment with 300 mg of magnesium oxide per day for 1 month significantly decreased both systolic (the top number) and diastolic (the bottom number) blood pressure (23).

Researchers theorize that the supplement may lower blood pressure by decreasing cellular calcium levels to relax smooth muscle cells and widen blood vessels (23).

May lower blood sugar levels

Magnesium supplements may lower blood sugar levels in people with diabetes.

For example, supplements containing magnesium oxide and zinc have been shown to lower blood sugar levels in people with type 1 diabetes, type 2 diabetes, and gestational diabetes, which is diabetes that can occur during pregnancy (24).

In a 2015 study, 70 women with gestational diabetes supplemented with either 250 mg of magnesium oxide or a placebo daily for 6 weeks (25).

The magnesium oxide treatment significantly improved blood sugar levels. It also reduced triglyceride levels and the inflammatory markers C-reactive protein (CRP) and malondialdehyde, compared with the placebo group (25).

Magnesium oxide supplements have also been shown to improve blood sugar management in Egyptian children with type 1 diabetes and Iranian adults with type 2 diabetes (26, 27).

Summary

Magnesium oxide may help treat migraine and constipation, reduce blood pressure, improve blood sugar management, and decrease levels of stress and anxiety in certain populations.

While supplementing with magnesium oxide may offer some benefits, there are potential side effects to consider.

Magnesium oxide is generally safe when used in appropriate doses. However, taking large amounts over long periods can lead to high blood magnesium levels, or hypermagnesemia, which is a serious condition that can be fatal (28, 29).

Groups particularly at risk of developing hypermagnesemia include those with kidney disease, older adults with bowel disorders, and those taking 1,000 mg of magnesium oxide or more per day (28, 30).

A 2019 case series discussed four cases of hypermagnesemia, one of which was fatal. All of the patients were over 65 years old and had kidney disease (30).

As such, researchers urge healthcare professionals to be aware of this risk and monitor magnesium levels in those being treated with magnesium oxide and other forms of magnesium (30).

Magnesium oxide may also result in digestive side effects like bloating and diarrhea, especially when taken at higher doses (31, 32).

What’s more, the supplement may suppress the absorption of certain medications, including antipsychotic and antidepressant drugs, as well as those used to treat urinary incontinence and Parkinson’s disease (33, 34, 35).

If you’re interested in taking magnesium oxide, consult your healthcare professional to determine whether it’s appropriate and safe for you.

Summary

High doses of magnesium oxide may cause dangerously high blood magnesium levels, which is more likely in specific populations. It may also cause side effects like bloating and diarrhea and reduce the effectiveness of certain medications.

How much magnesium oxide to take depends on the treatment purpose.

For example, magnesium oxide is used to prevent migraine with daily 500-mg doses (12).

Meanwhile, 300 mg per day has been shown to help treat high blood pressure, while 250 mg per day may help lower blood sugar levels in women with gestational diabetes (23, 25).

Higher doses of the supplement — usually over 1 gram — are used to treat constipation, though daily doses as low as 250 mg may be enough for some people (5).

Summary

Magnesium oxide dosing generally ranges from 250–1,000 mg per day depending on what it’s being used to treat. Taking too much can be dangerous. Speak with your healthcare professional if you have questions regarding dosing or side effects.

Magnesium oxide is a form of magnesium commonly taken as a dietary supplement. It has a lower bioavailability than other forms of magnesium, but it may still offer benefits.

Mainly, it’s used to treat migraine and constipation. It may also help reduce blood pressure, blood sugar, and anxiety in certain populations.

Taking too much magnesium is dangerous and can cause elevated blood magnesium levels, digestive side effects, and hindered absorption of certain medications.

If you’re interested in supplementing with magnesium oxide, consult your healthcare professional first to find out if it’s the right choice for you.