Magnesium Oxide
Also known as: MgO, magnesia, magnesium oxide
Randomized trials show magnesium oxide is more effective than placebo for chronic constipation. A small crossover trial in patients with ileal resection found magnesium oxide to have relatively low absorption compared with a chelated form in those with severe malabsorption. In a 24-week trial in overweight older adults, magnesium oxide (given to provide ~450 mg elemental magnesium daily) did not change arterial stiffness or blood pressure compared with placebo.
Last reviewed: 2026-10-14 · 4 indexed studies
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Overview
Magnesium oxide is a widely used oral magnesium salt sold as a dietary supplement and as an osmotic laxative. Clinical trials have tested it for treatment of chronic constipation and as a source of magnesium in people with impaired absorption.
Mechanism & Function
Mechanism of Action
As an osmotic agent in the gut, magnesium oxide draws water into the intestinal lumen, increasing stool liquidity and transit. Systemically it provides magnesium ions that participate in enzymatic reactions, nerve and muscle function and electrolyte balance.
Physiological Role
Source of magnesium for biochemical cofactors, neuromuscular transmission and electrolyte homeostasis; locally in the gut acts osmotically to increase water content of stool.
Primary Pathways
Performance / Health Relevance
Evidence from the provided trials does not support a role for magnesium oxide in improving arterial stiffness or blood pressure; performance-relevant benefits (eg. exercise recovery) are not addressed in the provided human trials.
Evidence Review
Compare Magnesium Forms
Full comparison5 magnesium forms are indexed. Bioavailability, clinical evidence, and best-use cases differ meaningfully between them.
| Form | Evidence |
|---|---|
Magnesium OxideThis page In patients with marked intestinal malabsorption (ileal resection), magnesium oxide showed lower absorption compared with a magnesium diglycinate chelate in a crossover study (7815675). | 52/100 |
| Magnesium Glycinate Glycinate chelation provides ~80% relative bioavailability vs ~4% for magnesium oxide. | 84/100 |
| Magnesium Citrate ~25–30% absorption — superior to oxide; below glycinate for neurological endpoints. | 70/100 |
| Aquamin Mg Comparable to other Mg hydroxide forms. | 58/100 |
| Magnesium L-Threonate Described by the developers and trial abstracts as having superior ability to raise brain magnesium concentrations compared with other magnesium salts. | 54/100 |
Practical Use & Dosage
- Minimum Effective Dose
- Magnesium oxide 1.5 g daily was effective for chronic constipation in a randomized trial (32969946).
- Optimal Range
- Not established from the provided trials. Another trial used magnesium formulations delivering ~450 mg elemental magnesium daily for 24 weeks (35253448).
- Upper / Caution Level
- Not established from the provided abstracts; caution advised in renal impairment due to risk of magnesium accumulation.
- Timing
- Oral administration as used in trials (daily). Specific timing relative to meals not specified in the provided abstracts.
- Best Format
- Oral tablets or powder (standard over-the-counter formulations used in trials).
- Bioavailability
- In patients with marked intestinal malabsorption (ileal resection), magnesium oxide showed lower absorption compared with a magnesium diglycinate chelate in a crossover study (7815675).
- Absorption Considerations
- Absorption can be poor with magnesium oxide in people with impaired intestinal function; systemic accumulation risk increases with renal impairment.
Safety & Interactions
Side Effects
- •Loose stools or diarrhoea
- •Abdominal discomfort/cramping
Contraindications
- Severe renal impairment (risk of magnesium accumulation)
Drug Interactions
- •Not detailed in provided abstracts; consider interaction risk in persons on multiple medications but specifics not provided here.
Who Should Avoid
- •People with severe renal impairment
- •Those advised to avoid osmotic laxatives without medical review
Monitoring
Monitor for signs of diarrhoea or dehydration; monitor renal function and serum magnesium if there is concern about accumulation.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Magnesium Oxide typically used or indicated?
Magnesium Oxide is most commonly used for: Oral magnesium supplementation, Osmotic laxative for constipation, Dietary magnesium source. Source of magnesium for biochemical cofactors, neuromuscular transmission and electrolyte homeostasis; locally in the gut acts osmotically to increase water content of stool.
How does Magnesium Oxide work?
As an osmotic agent in the gut, magnesium oxide draws water into the intestinal lumen, increasing stool liquidity and transit. Systemically it provides magnesium ions that participate in enzymatic reactions, nerve and muscle function and electrolyte balance.
What is the recommended dose of Magnesium Oxide?
The optimal range is Not established from the provided trials. Another trial used magnesium formulations delivering ~450 mg elemental magnesium daily for 24 weeks (35253448).. with a minimum effective dose of Magnesium oxide 1.5 g daily was effective for chronic constipation in a randomized trial (32969946).. Best taken: Oral administration as used in trials (daily). Specific timing relative to meals not specified in the provided abstracts.. Upper / caution level: Not established from the provided abstracts; caution advised in renal impairment due to risk of magnesium accumulation..
What are the side effects of Magnesium Oxide?
Reported side effects include: Loose stools or diarrhoea; and Abdominal discomfort/cramping. Monitoring: Monitor for signs of diarrhoea or dehydration; monitor renal function and serum magnesium if there is concern about accumulation.
Does Magnesium Oxide interact with medications?
Known or theoretical interactions: Not detailed in provided abstracts; consider interaction risk in persons on multiple medications but specifics not provided here.. Always check with a clinician before combining with prescription medication.
Who should avoid Magnesium Oxide?
Magnesium Oxide is generally not recommended for: People with severe renal impairment; Those advised to avoid osmotic laxatives without medical review; and Severe renal impairment (risk of magnesium accumulation).
How strong is the evidence for Magnesium Oxide?
Evidence level: Limited (overall score 52/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
Senna Versus Magnesium Oxide for the Treatment of Chronic Constipation: A Randomized, Placebo-Controlled Trial.
Randomized, double-blind, placebo-controlled trial comparing senna (1.0 g), magnesium oxide (1.5 g) and placebo for 28 days in adults with chronic idiopathic constipation.
Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection.
Double-blind, randomized crossover trial in 12 patients with ileal resection comparing bioavailability of 26Mg-labeled magnesium diglycinate vs 26Mg-labeled magnesium oxide (100 mg dose).
Effects of Magnesium Citrate, Magnesium Oxide, and Magnesium Sulfate Supplementation on Arterial Stiffness: A Randomized, Double-Blind, Placebo-Controlled Intervention Trial.
Randomized, double-blind, placebo-controlled trial assessing effects of magnesium citrate, magnesium oxide, and magnesium sulfate (providing 450 mg elemental magnesium daily) versus placebo on arterial stiffness and blood pressure over 24 weeks in overweight slightly obese adults.
Pharmacological prevention and treatment of opioid-induced constipation in cancer patients: A systematic review and meta-analysis.
Systematic review and meta-analysis of pharmacological prevention and treatment of opioid-induced constipation in cancer patients; included randomized trials and cohort studies and compared various laxatives and opioid antagonists.
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Sodium Citrate
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Pink Himalayan Salt
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Research Overview
Limited EvidenceCite this ingredient
One-click citation export in APA, MLA, Chicago, BibTeX, or HTML. The URL below is stable and safe to link.
Stable URL
https://thesuppindex.com/ingredients/magnesium-oxide
SuppIndex. (2026). Magnesium Oxide: Evidence summary, dosage and clinical studies. Retrieved October 16, 2026, from https://thesuppindex.com/ingredients/magnesium-oxide
Based on 4 indexed studies · Evidence level: Limited.
Goal Ratings
Stack Compatibility
Can be combined with other oral magnesium forms but watch total elemental magnesium intake and gastrointestinal tolerability.