What is magnesium oxide

Magnesium is an abundant mineral in the body and magnesium is naturally present in many foods, added to other food products, available as a dietary supplement, and present in some medicines (such as antacids and laxatives). Magnesium oxide may be used for different reasons with some people using it as an antacid to relieve heartburn, sour stomach, or acid indigestion. Magnesium oxide also may be used as a laxative for short-term, rapid emptying of the bowel (before surgery, for example). Magnesium oxide should not be used repeatedly. Magnesium oxide also is used as a dietary supplement when the amount of magnesium in the diet is not enough. Magnesium oxide is available without a prescription.

Magnesium is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation 1). Magnesium is required for energy production, oxidative phosphorylation, and glycolysis. Magnesium contributes to the structural development of bone and is required for the synthesis of DNA, RNA, and the antioxidant glutathione. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm 2).

The total magnesium content of the human body is reported to be ~20 mmol/kg of fat-free tissue. In other words, total magnesium in the average 70 kg adult with 20% (w/w) fat is ~1000 to 1120 mmol or approximately 25 g magnesium, with 50% to 60% present in the bones and most of the rest in soft tissues 3). About 99% of total body magnesium is located in bone, muscles and non-muscular soft tissue. Less than 1% of total magnesium is in blood serum, and these levels are kept under tight control. Magnesium excretion is mainly regulated by the kidney. About 100 mmol/L magnesium is filtered daily 4). Normal serum magnesium concentrations range between 0.75 and 0.95 millimoles (mmol)/L 5). Hypomagnesemia is defined as a serum magnesium level less than 0.75 mmol/L 6). Magnesium homeostasis is largely controlled by the kidney, which typically excretes about 120 mg magnesium into the urine each day 7). Urinary excretion is reduced when magnesium status is low 8).

Magnesium is widely distributed in plant and animal foods and in beverages (see Table 2). Green leafy vegetables, such as spinach, legumes, nuts, seeds, and whole grains, are good sources 9). Water accounts for ~10% of daily magnesium intake 10), chlorophyll (and thus green vegetables such as spinach) is the major source of magnesium. Nuts, seeds and unprocessed cereals are also rich in magnesium. Legumes, fruit, fish and meat have an intermediate magnesium concentration. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially. Low magnesium concentrations are found in dairy products, except milk 11). In general, foods containing dietary fiber provide magnesium. Magnesium is also added to some breakfast cereals and other fortified foods. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially 12). Selected food sources of magnesium are listed in Table 2.

Tap, mineral, and bottled waters can also be sources of magnesium, but the amount of magnesium in water varies by source and brand (ranging from 1 mg/L to more than 120 mg/L) 13).

Approximately 30% to 40% of the dietary magnesium consumed is typically absorbed by the body 14).

Assessing magnesium status is difficult because most magnesium is inside cells or in bone 15). The most commonly used and readily available method for assessing magnesium status is measurement of serum magnesium concentration, even though serum levels have little correlation with total body magnesium levels or concentrations in specific tissues 16). Other methods for assessing magnesium status include measuring magnesium concentrations in erythrocytes, saliva, and urine; measuring ionized magnesium concentrations in blood, plasma, or serum; and conducting a magnesium-loading (or “tolerance”) test. No single method is considered satisfactory 17). Some experts 18) but not others 19) consider the tolerance test (in which urinary magnesium is measured after parenteral infusion of a dose of magnesium) to be the best method to assess magnesium status in adults. To comprehensively evaluate magnesium status, both laboratory tests and a clinical assessment might be required 20).

Table 1: Recommended Dietary Allowances (RDAs) for Magnesium

Birth to 6 months30 mg*30 mg*
7–12 months75 mg*75 mg*
1–3 years80 mg80 mg
4–8 years130 mg130 mg
9–13 years240 mg240 mg
14–18 years410 mg360 mg400 mg360 mg
19–30 years400 mg310 mg350 mg310 mg
31–50 years420 mg320 mg360 mg320 mg
51+ years420 mg320 mg

Footnote: *Adequate Intake (AI) = Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an Recommended Dietary Allowance (average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.).

[Source 21)]

Table 2: Selected food sources of magnesium

(mg) per
Almonds, dry roasted, 1 ounce8020
Spinach, boiled, ½ cup7820
Cashews, dry roasted, 1 ounce7419
Peanuts, oil roasted, ¼ cup6316
Cereal, shredded wheat, 2 large biscuits6115
Soymilk, plain or vanilla, 1 cup6115
Black beans, cooked, ½ cup6015
Edamame, shelled, cooked, ½ cup5013
Peanut butter, smooth, 2 tablespoons4912
Bread, whole wheat, 2 slices4612
Avocado, cubed, 1 cup4411
Potato, baked with skin, 3.5 ounces4311
Rice, brown, cooked, ½ cup4211
Yogurt, plain, low fat, 8 ounces4211
Breakfast cereals, fortified with 10% of the DV for magnesium4010
Oatmeal, instant, 1 packet369
Kidney beans, canned, ½ cup359
Banana, 1 medium328
Salmon, Atlantic, farmed, cooked, 3 ounces267
Milk, 1 cup24–276–7
Halibut, cooked, 3 ounces246
Raisins, ½ cup236
Chicken breast, roasted, 3 ounces226
Beef, ground, 90% lean, pan broiled, 3 ounces205
Broccoli, chopped and cooked, ½ cup123
Rice, white, cooked, ½ cup103
Apple, 1 medium92
Carrot, raw, 1 medium72

Footnotes: *DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration (FDA) to help consumers compare the nutrient contents of products within the context of a total diet. The DV for magnesium is 400 mg for adults and children aged 4 and older. However, the FDA does not require food labels to list magnesium content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient.

[Source 22)]

Magnesium oxide supplement

Magnesium oxide supplement is available in a variety of forms, including magnesium oxide, magnesium citrate, and magnesium chloride 23). The Supplement Facts panel on a dietary supplement label declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound.

Absorption of magnesium from different kinds of magnesium supplements varies. Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms 24). Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate 25). One study found that very high doses of zinc from supplements (142 mg/day) can interfere with magnesium absorption and disrupt the magnesium balance in the body 26).

Magnesium oxide vs Magnesium citrate

Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate 27). Just like  magnesium oxide, magnesium citrate is also used to treats constipation, and empties the bowel before surgery or other medical procedures. Magnesium citrate is a low-volume osmotic laxative that is effective in small-volume bowel preparation. The 8-oz (237 mL) magnesium citrate solution consisted of magnesium carbonate (31%), citric acid (65%), and potassium citrate (3%), yielding 18.0 g of magnesium citrate (e.g., LoSo Prep; E-Z-Em).

Magnesium oxide uses

What is magnesium oxide used for

  • Magnesium oxide is used to treat or prevent low magnesium levels.
  • Magnesium oxide is used to treat heartburn and upset stomach.
  • Magnesium oxide is used as laxative to relieve occasional constipation.

You should not use magnesium oxide if you are allergic to it.

Ask a doctor or pharmacist if it is safe for you to use magnesium oxide if you have other medical conditions, especially:

  • kidney disease;
  • heart disease;
  • nausea, vomiting;
  • a blockage in your intestines;
  • low levels of calcium in your blood; or
  • a sudden change in bowel habits for 2 weeks or longer.

It is not known whether magnesium oxide will harm an unborn baby. Ask a doctor before using this medicine if you are pregnant.

It is not known whether magnesium oxide passes into breast milk or if it could affect a nursing baby. Ask a doctor before using this medicine if you are breast-feeding.

Do not give this medicine to a child without medical advice.

Magnesium oxide should not be given to a child younger than 6 years old.

Magnesium benefits

Magnesium for ADHD

Attention deficit hyperactivity disorder (ADHD) is the most common psychiatric disorder in clinical samples of children and adolescents referring to child psychiatric clinics. Dietary factors can play a significant role in the etiology of attention deficit hyperactivity disorder (ADHD). Several studies reported that the magnesium level in children with ADHD is decreased in serum and erythrocytes and the Mg2+-ATPase activity is reduced 28). Treatment of magnesium deficiency can help in revealing hyperactivity in children [126,127,128,129,130]. Current treatments for ADHD, such as atomoxetine and stimulants, act through adrenergic and dopaminergic receptors. Magnesium interacts with the ADHD-related neurotransmitters (e.g., dopamine, serotonin) and inhibits N-methyl-d-aspartate (NMDA)-induced norepinephrine release. The results of several studies are promising that magnesium supplementation (e.g. 6 mg/kg BW per day) may be helpful in the treatment of ADHD 29). Unfortunately, until now there is still no double-blind randomized controlled clinical trial investigating the efficacy and safety of magnesium for treating ADHD.

Magnesium for osteoporosis

Magnesium is involved in bone formation and influences the activities of osteoblasts and osteoclasts 30). Magnesium also affects the concentrations of both parathyroid hormone and the active form of vitamin D, which are major regulators of bone homeostasis. Several population-based studies have found positive associations between magnesium intake and bone mineral density in both men and women 31). Other research has found that women with osteoporosis have lower serum magnesium levels than women with osteopenia and those who do not have osteoporosis or osteopenia 32). These and other findings indicate that magnesium deficiency might be a risk factor for osteoporosis 33).

Although limited in number, studies suggest that increasing magnesium intakes from food or supplements might increase bone mineral density in postmenopausal and elderly women 34). For example, one short-term study found that 290 mg/day elemental magnesium (as magnesium citrate) for 30 days in 20 postmenopausal women with osteoporosis suppressed bone turnover compared with placebo, suggesting that bone loss decreased 35).

Diets that provide recommended levels of magnesium enhance bone health, but further research is needed to elucidate the role of magnesium in the prevention and management of osteoporosis.

Magnesium for migraines and headaches

Magnesium deficiency is related to factors that promote headaches, including neurotransmitter release and vasoconstriction 36). People who experience migraine headaches have lower levels of serum and tissue magnesium than those who do not.

However, research on the use of magnesium supplements to prevent or reduce symptoms of migraine headaches is limited. Three of four small, short-term, placebo-controlled trials found modest reductions in the frequency of migraines in patients given up to 600 mg/day magnesium 37). The authors of a review on migraine prophylaxis 38) suggested that taking 300 mg magnesium twice a day, either alone or in combination with medication, can prevent migraines.

In their evidence-based guideline update, the American Academy of Neurology and the American Headache Society concluded that magnesium therapy is “probably effective” for migraine prevention 39). Because the typical dose of magnesium used for migraine prevention exceeds the Tolerable Upper Intake Level (maximum daily intake unlikely to cause adverse health effects), this treatment should be used only under the direction and supervision of a healthcare provider.

Magnesium for hypertension and cardiovascular disease

Hypertension is a major risk factor for heart disease and stroke. Studies to date, however, have found that magnesium supplementation lowers blood pressure, at best, to only a small extent. A meta-analysis of 12 clinical trials found that magnesium supplementation for 8–26 weeks in 545 hypertensive participants resulted in only a small reduction (2.2 mmHg) in diastolic blood pressure 40). The dose of magnesium ranged from approximately 243 to 973 mg/day. The authors of another meta-analysis of 22 studies with 1,173 normotensive and hypertensive adults concluded that magnesium supplementation for 3–24 weeks decreased systolic blood pressure by 3–4 mmHg and diastolic blood pressure by 2–3 mmHg 41). The effects were somewhat larger when supplemental magnesium intakes of the participants in the nine crossover-design trials exceeded 370 mg/day. A diet containing more magnesium because of added fruits and vegetables, more low-fat or non-fat dairy products, and less fat overall was shown to lower systolic and diastolic blood pressure by an average of 5.5 and 3.0 mmHg, respectively 42). However, this Dietary Approaches to Stop Hypertension (DASH) diet also increases intakes of other nutrients, such as potassium and calcium, that are associated with reductions in blood pressure, so any independent contribution of magnesium cannot be determined.

Several prospective studies have examined associations between magnesium intakes and heart disease. The Atherosclerosis Risk in Communities study assessed heart disease risk factors and levels of serum magnesium in a cohort of 14,232 white and African-American men and women aged 45 to 64 years at baseline 43). Over an average of 12 years of follow-up, individuals in the highest quartile of the normal physiologic range of serum magnesium (at least 0.88 mmol/L) had a 38% reduced risk of sudden cardiac death compared with individuals in the lowest quartile (0.75 mmol/L or less). However, dietary magnesium intakes had no association with risk of sudden cardiac death. Another prospective study tracked 88,375 female nurses in the United States to determine whether serum magnesium levels measured early in the study and magnesium intakes from food and supplements assessed every 2 to 4 years were associated with sudden cardiac death over 26 years of follow-up 44). Women in the highest compared with the lowest quartile of ingested and plasma magnesium concentrations had a 34% and 77% lower risk of sudden cardiac death, respectively. Another prospective population study of 7,664 adults aged 20 to 75 years in the Netherlands who did not have cardiovascular disease found that low urinary magnesium excretion levels (a marker for low dietary magnesium intake) were associated with a higher risk of ischemic heart disease over a median follow-up period of 10.5 years. Plasma magnesium concentrations were not associated with risk of ischemic heart disease 45). A systematic review and meta-analysis of prospective studies found that higher serum levels of magnesium were significantly associated with a lower risk of cardiovascular disease, and higher dietary magnesium intakes (up to approximately 250 mg/day) were associated with a significantly lower risk of ischemic heart disease caused by a reduced blood supply to the heart muscle 46).

Higher magnesium intakes might reduce the risk of stroke. In a meta-analysis of 7 prospective trials with a total of 241,378 participants, an additional 100 mg/day magnesium in the diet was associated with an 8% decreased risk of total stroke, especially ischemic rather than hemorrhagic stroke 47). One limitation of such observational studies, however, is the possibility of confounding with other nutrients or dietary components that could also affect the risk of stroke.

A large, well-designed clinical trial is needed to better understand the contributions of magnesium from food and dietary supplements to heart health and the primary prevention of cardiovascular disease 48).

Magnesium for type 2 diabetes

Diets with higher amounts of magnesium are associated with a significantly lower risk of diabetes, possibly because of the important role of magnesium in glucose metabolism 49). Hypomagnesemia might worsen insulin resistance, a condition that often precedes diabetes, or it might be a consequence of insulin resistance 50). Diabetes leads to increased urinary losses of magnesium, and the subsequent magnesium inadequacy might impair insulin secretion and action, thereby worsening diabetes control 51).

Most investigations of magnesium intake and risk of type 2 diabetes have been prospective cohort studies. A meta-analysis of 7 of these studies, which included 286,668 patients and 10,912 cases of diabetes over 6 to 17 years of follow-up, found that a 100 mg/day increase in total magnesium intake decreased the risk of diabetes by a statistically significant 15% 52). Another meta-analysis of 8 prospective cohort studies that followed 271,869 men and women over 4 to 18 years found a significant inverse association between magnesium intake from food and risk of type 2 diabetes; the relative risk reduction was 23% when the highest to lowest intakes were compared 53).

A 2011 meta-analysis of prospective cohort studies of the association between magnesium intake and risk of type 2 diabetes included 13 studies with a total of 536,318 participants and 24,516 cases of diabetes 54). The mean length of follow-up ranged from 4 to 20 years. Investigators found an inverse association between magnesium intake and risk of type 2 diabetes in a dose-responsive fashion, but this association achieved statistical significance only in overweight (body mass index [BMI] 25 or higher) but not normal-weight individuals (BMI less than 25). Again, a limitation of these observational studies is the possibility of confounding with other dietary components or lifestyle or environmental variables that are correlated with magnesium intake.

Only a few small, short-term clinical trials have examined the potential effects of supplemental magnesium on control of type 2 diabetes and the results are conflicting 55). For example, 128 patients with poorly controlled diabetes in a Brazilian clinical trial received a placebo or a supplement containing either 500 mg/day or 1,000 mg/day magnesium oxide (providing 300 or 600 mg elemental magnesium, respectively) 56). After 30 days of supplementation, plasma, cellular, and urine magnesium levels increased in participants receiving the larger dose of the supplement, and their glycemic control improved. In another small trial in Mexico, participants with type 2 diabetes and hypomagnesemia who received a liquid supplement of magnesium chloride (providing 300 mg/day elemental magnesium) for 16 weeks showed significant reductions in fasting glucose and glycosylated hemoglobin concentrations compared with participants receiving a placebo, and their serum magnesium levels became normal 57). In contrast, neither a supplement of magnesium aspartate (providing 369 mg/day elemental magnesium) nor a placebo taken for 3 months had any effect on glycemic control in 50 patients with type 2 diabetes who were taking insulin 58).

The American Diabetes Association states that there is insufficient evidence to support the routine use of magnesium to improve glycemic control in people with diabetes 59). It further notes that there is no clear scientific evidence that vitamin and mineral supplementation benefits people with diabetes who do not have underlying nutritional deficiencies.

Magnesium oxide dosage

Use magnesium oxide exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Take magnesium oxide with a full glass of water.

When using magnesium oxide as a laxative, it may be best to take your dose at bedtime.

Magnesium oxide may be taken with food if it upsets your stomach.

Call your doctor if your symptoms do not improve after 7 days of treatment, or if symptoms get worse.

Store at room temperature away from moisture and heat.

Magnesium oxide can make it harder for your body to absorb other medicines you take by mouth. Avoid taking other medicines within 2 hours before or 2 hours after you take magnesium oxide. You may need to wait 4 hours to take your other medicines after taking magnesium oxide. Ask your doctor how to best schedule your medications.

Adult dose for dyspepsia

Uses: Acid indigestion, upset stomach

  • 400 mg tablets: 1 tablet orally twice a day
  • Maximum dose: 2 tablets per 24 hour period
  • Duration of therapy: Up to 2 weeks


  • May have a laxative effect.

Adult dose for constipation

  • Oral: Caplets (500 mg): 2 to 4 caplets orally daily with a full 8 ounce glass of liquid.
  • Caplets may be taken all at bedtime or separately throughout the day.

Adult dose for vitamin/mineral supplementation during pregnancy/lactation

Recommended dietary intake:

  • Women 19 to 30 years: 508 mg magnesium oxide (310 mg elemental magnesium) orally daily
  • Women 31 years and older: 525 mg magnesium oxide (320 mg elemental magnesium) orally daily
  • Men 19 to 30 years: 656 mg magnesium oxide (400 mg elemental magnesium) orally daily
  • Men 31 years and older: 689 mg magnesium oxide (420 mg elemental) orally daily

Maximum magnesium oxide supplement dose: 574 mg magnesium oxide (350 mg elemental magnesium)

Pediatric dose for constipation

500 mg caplets:

  • 12 years and older: 2 to 4 caplets orally daily, as a single dose or divided dose
  • Maximum dose: 4 caplets per day
  • Duration of therapy: 7 days or less


-Bedtime is the preferred administration time for a single dose.
-Take with a full glass of water.

Pediatric dose for vitamin/mineral supplementation

Recommended dietary intakes:

  • 14 to 18 years:
  • Males: 672 mg magnesium oxide (410 mg elemental magnesium) per day
  • Females: 590 mg magnesium oxide (360 mg elemental magnesium) per day

Maximum magnesium oxide supplement dose (both sexes): 574 mg magnesium oxide (350 mg elemental magnesium) per day

9 to 13 years: 394 mg magnesium oxide (240 mg elemental) per day

  • Maximum magnesium oxide supplement dose: 574 mg magnesium oxide (350 mg elemental magnesium) per day

4 to 8 years: 213 mg magnesium oxide (130 mg elemental magnesium) per day

  • Maximum magnesium oxide supplement dose: 180 mg magnesium oxide (110 mg elemental magnesium) per day

1 to 3 years: 131 mg magnesium oxide (80 mg elemental) per day

  • Maximum magnesium oxide supplement dose: 107 mg magnesium oxide (65 mg elemental magnesium) per day

7 to 12 months: 123 mg magnesium oxide (75 mg elemental magnesium) per day

Birth to 6 months: 49 mg magnesium oxide (30 mg elemental magnesium) per day

Magnesium oxide side effects

Too much magnesium from food does not pose a health risk in healthy individuals because the kidneys eliminate excess amounts in the urine 60). However, high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping 61). Forms of magnesium most commonly reported to cause diarrhea include magnesium carbonate, chloride, gluconate, and oxide 62). The diarrhea and laxative effects of magnesium salts are due to the osmotic activity of unabsorbed salts in the intestine and colon and the stimulation of gastric motility.

Very large doses of magnesium-containing laxatives and antacids (typically providing more than 5,000 mg/day magnesium) have been associated with magnesium toxicity 63), including fatal hypermagnesemia in a 28-month-old boy 64) and an elderly man 65). Symptoms of magnesium toxicity, which usually develop after serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, retention of urine, ileus, depression, and lethargy before progressing to muscle weakness, difficulty breathing, extreme hypotension, irregular heartbeat, and cardiac arrest 66). The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost 67).

Magnesium oxide may cause side effects. To avoid unpleasant taste, take the tablet with citrus fruit juice or carbonated citrus drink. Tell your doctor if either of these symptoms are severe or do not go away:

  • cramping
  • diarrhea

If you experience any of the following symptoms, call your doctor immediately:

  • rash or hives
  • itching
  • dizziness or lightheadedness
  • mood or mental changes
  • unusual tiredness
  • weakness
  • nausea
  • vomiting

Interactions with Medications

Several types of medications have the potential to interact with magnesium supplements or affect magnesium status. A few examples are provided below. People taking these and other medications on a regular basis should discuss their magnesium intakes with their healthcare providers.


Magnesium-rich supplements or medications can decrease the absorption of oral bisphosphonates, such as alendronate (Fosamax®), used to treat osteoporosis 68). Use of magnesium-rich supplements or medications and oral bisphosphonates should be separated by at least 2 hours.


Magnesium can form insoluble complexes with tetracyclines, such as demeclocycline (Declomycin®) and doxycycline (Vibramycin®), as well as quinolone antibiotics, such as ciprofloxacin (Cipro®) and levofloxacin (Levaquin®). These antibiotics should be taken at least 2 hours before or 4–6 hours after a magnesium-containing supplement 69).


Chronic treatment with loop diuretics, such as furosemide (Lasix®) and bumetanide (Bumex®), and thiazide diuretics, such as hydrochlorothiazide (Aquazide H®) and ethacrynic acid (Edecrin®), can increase the loss of magnesium in urine and lead to magnesium depletion 70). In contrast, potassium-sparing diuretics, such as amiloride (Midamor®) and spironolactone (Aldactone®), reduce magnesium excretion 71).

Proton pump inhibitors

Prescription proton pump inhibitor (PPI) drugs, such as esomeprazole magnesium (Nexium®) and lansoprazole (Prevacid®), when taken for prolonged periods (typically more than a year) can cause hypomagnesemia. In cases that FDA reviewed, magnesium supplements often raised the low serum magnesium levels caused by PPIs. However, in 25% of the cases, supplements did not raise magnesium levels and the patients had to discontinue the PPI. FDA advises healthcare professionals to consider measuring patients’ serum magnesium levels prior to initiating long-term PPI treatment and to check magnesium levels in these patients periodically.

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