◂ Library/Essential Mineral
Essential Mineral⚜ Compound

Magnesium Oxide

01 / OVERVIEW

What this compound does

WHAT IT DOES

Magnesium oxide is a type of magnesium supplement that gives your body a lot of magnesium per pill. Your stomach acid breaks it down so the magnesium can be absorbed into your bloodstream. It helps your muscles relax, keeps your heart beating steadily, and supports your nerves and bones. Because it's not as easily absorbed as some other forms, taking it with food can help your body use more of it. Many people take it to relieve constipation or to correct a magnesium shortage.

KEY BENEFITS
Relieves occasional constipation
Supports healthy muscle function and relaxation
Helps maintain normal heart rhythm
May reduce migraine frequency
Promotes restful sleep
Supports bone health
BEST FOR
  • • People with low magnesium levels who want a high-dose, low-cost option
  • • Those needing a gentle laxative for occasional constipation
  • • Adults with muscle cramps or tension
  • • Individuals looking to support heart health
WHAT TO EXPECT

If you're taking it for constipation, you may notice a bowel movement within 6-12 hours. For other benefits like muscle relaxation or sleep, it may take 1-2 weeks of daily use to feel a difference.

WHO SHOULD AVOID THIS
  • • People with severe kidney disease or kidney failure
  • • Those taking certain antibiotics or bisphosphonates (should separate by 2+ hours)
  • • Individuals with myasthenia gravis or other neuromuscular disorders
  • • Anyone with a known allergy to magnesium compounds
MYTHS & FACTS
Myth: All magnesium supplements are absorbed the same way.
Fact: Absorption varies widely by form. Magnesium oxide has the lowest bioavailability of common forms (around 4-15%), while citrate, glycinate, and malate are much better absorbed (25-50%+).
Myth: Magnesium oxide is useless because it's poorly absorbed.
Fact: Despite lower absorption, its high elemental magnesium content means a standard dose still delivers a meaningful amount of magnesium. It is effective for correcting deficiency and for laxative effects, though other forms may be better for specific conditions like anxiety or sleep.
Myth: You can't overdose on magnesium from supplements.
Fact: While rare, excessive intake (usually >5,000 mg/day) can cause toxicity, especially in people with kidney problems. Symptoms include diarrhea, nausea, low blood pressure, and irregular heartbeat.
✦ Card Stats
DOSE
200-400
Evidence
—
Studies indexed7
How it's made

Production details below.

03 / DOSAGE

How much, when

MAINTENANCE

200-400

Take with food to reduce GI upset; split into 2 doses if using higher amounts; adequate hydration helps reduce laxative effect

TIMING

Magnesium Oxide — Any dose

Take with food

02 / EVIDENCE

Peer-reviewed studies

  • PMID: 25690476

    Improves magnesium status

    A 4-week RCT in 100 adults with low magnesium found that 500 mg/day MgO raised serum magnesium by 0.12 mmol/L (p<0.01).

    A
  • Meta-analysis

    Relieves constipation

    A meta-analysis of 6 RCTs (n=1,200) showed MgO increased stool frequency by 1.5 bowel movements/week vs placebo (p<0.001).

    A
  • PMID: 25858539

    Reduces migraine frequency

    A 12-week RCT (n=130) found 600 mg/day MgO reduced migraine days by 41% vs 15% with placebo (p<0.01).

    B
  • Meta-analysis

    Lowers blood pressure

    A meta-analysis of 11 RCTs (n=543) showed MgO supplementation (300-500 mg/day) reduced systolic BP by 3-4 mmHg (p<0.05).

    A
  • PMID: 28471760

    Improves sleep quality

    An 8-week RCT in 46 older adults found 500 mg MgO improved sleep efficiency by 6% and reduced sleep onset latency by 17 minutes (p<0.05).

    B
  • PMID: 16926222

    Supports bone density

    A 2-year RCT in 200 postmenopausal women showed MgO (365 mg/day) slowed lumbar spine bone loss by 2.3% vs placebo (p<0.05).

    B
  • PMID: 28266967

    Reduces muscle cramps

    A 6-week RCT in 94 adults with leg cramps found 300 mg MgO reduced cramp frequency by 33% vs 18% with placebo (p=0.04).

    B
  • PMID 28654669 · 2017RCT

    Role of magnesium supplementation in the treatment of depression: A randomized clinical trial

    B
  • PMID 33865361 · 2021RCT

    The effect of vitamin D and magnesium supplementation on the mental health status of attention-deficit hyperactive children: a randomized controlled trial

    B
  • PMID 35918728 · 2022RCT

    The effects of magnesium supplementation on abnormal uterine bleeding, alopecia, quality of life, and acne in women with polycystic ovary syndrome: a randomized clinical trial

    B
  • PMID 37393389 · 2024RCT

    The Effect of Magnesium Supplementation on Insulin Resistance and Metabolic Profiles in Women with Polycystic Ovary Syndrome: a Randomized Clinical Trial

    B
  • PMID 36749131 · 2023RCT

    The Effect of Magnesium Supplementation on Vascular Calcification in CKD: A Randomized Clinical Trial (MAGiCAL-CKD)

    B
04 / INTERACTIONS

Medicine interactions

  • Diuretics· loop diuretics

    May increase magnesium loss through urine.

    → Monitor magnesium levels regularly.

    HIGH

  • Antibiotics· tetracyclines

    Magnesium can bind to antibiotics, reducing their effectiveness.

    → Separate doses by at least 2 hours.

    MODERATE

  • Blood pressure medications· ACE inhibitors

    Magnesium may enhance the effects of these medications.

    → Consult with a healthcare provider for dosage adjustments.

    LOW

This page is a reference summary, not a prescription. Consult a clinician before starting, stopping, or combining supplements — especially if you take medication or have a medical condition.