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📰Read the full Magnesium Oxide evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ ~4% absorption — 96% passes through unabsorbed [1]
⚠ Appropriate for constipation/antacid — NOT for correcting Mg deficiency [1]
⚠ '240 mg elemental Mg' on label is misleading — only ~10 mg absorbed [1]
⚠ Patient on MgO for deficiency — switch to glycinate or citrate [1]
ℹ️ Not obtained from food. Not applicable — this is not obtained from food in meaningful amounts; supplementation is the practical route.
🔬 Lab interpreter
Recommended test
See Mg entry
See Mg entry
If using MgO for 'Mg supplementation' — check if levels are actually improving. If not: switch forms [1].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
MgO: 60% elemental (highest), ~4% absorbed (worst). A 400 mg pill delivers ~10 mg to systemic circulation. It's a LAXATIVE and ANTACID, not a systemic Mg supplement. The cheapest form but the worst value per absorbed mg. For Mg deficiency: glycinate (80% absorbed). For constipation: MgO is actually appropriate [1].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: See guidance
Common antacid/laxative in pregnancy [1].
👦 Pediatric: See guidance
MoM used as pediatric laxative [1].
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Standard dose
How to take
🍽 Timing: Laxative: bedtime. Antacid: after meals [1].
💊 With food: Any [1].
🚫 Avoid: For systemic Mg supplementation [1].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Magnesium oxide capsules/tablets', 'common', '400 mg (240 mg elemental). Cheap. Poorly absorbed [1].'] | Standard | Check label | |
| ['Milk of Magnesia (Mg hydroxide)', '', 'Closely related. OTC laxative/antacid [1].'] | Standard | Check label |
3 Common questions
Why is MgO so popular if absorption is terrible? ▼
(1) Cheapest, (2) highest elemental Mg per pill (looks good on label — '240 mg per capsule'), (3) consumers don't know about absorption differences. Marketing of 'high elemental Mg' is misleading without absorption context [1].
When IS MgO appropriate? ▼
As a laxative (constipation) or antacid (heartburn/GERD). For these uses, you WANT it to stay in the GI tract [1].
Is MgO worthless for Mg deficiency? ▼
Nearly — ~96% passes through unabsorbed. Some Mg is absorbed, but you'd need very high doses to match what glycinate or citrate delivers. For correcting deficiency: switch forms [1].
4 Clinical evidence
Strong
~4% absorption: confirmed in multiple bioavailability studies [1]. Osmotic laxative mechanism: unabsorbed MgO draws water into intestinal lumen [1]. HIGH
Moderate
Constipation treatment: effective osmotic laxative [1]. Antacid: neutralizes gastric acid [1]. MODERATE
Insufficient
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Severe renal failure (GFR <30) — hypermagnesemia risk
✕ Bowel obstruction (its laxative action)
Relative
⚠ Low fractional absorption — poor choice for correcting deficiency
⚠ Marked laxative/loose-stool effect
⚠ Separate from tetracyclines, quinolones, bisphosphonates and from gastric-acid-dependent drugs
🚩 Red flags
● Patient using MgO for Mg deficiency — switch forms [1]
● Renal failure + high-dose MgO — hypermagnesemia risk [1]
6 Interactions
Drug interactions
7 US supplement products
6
on-market products containing Magnesium Oxide (NIH DSLD)
Brands carrying Magnesium Oxide (1)
Click a brand to see its Magnesium Oxide products.
8 Cite this page
Vancouver: Pkhakadze G. Magnesium Oxide — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Aug 15]. Available from: https://supplement.ge/ingredients/magnesium-oxide/
APA 7th: Pkhakadze, G. (2026). Magnesium Oxide — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/magnesium-oxide/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: February 2027
References: 1 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Magnesium Oxide — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/magnesium-oxide/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG