Magnesium Oxide: Dosage, Timing & Interactions

Check it against something

Evidence level A

Magnesium Oxide with:

94 out of 100

Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Cost-effective supplementation

Most affordable way to supplement with magnesium

High elemental magnesium content per dose reduces cost per mg Evidence A-grade Immediate economic benefit

High elemental magnesium content

Contains 60% elemental magnesium by weight

Simple oxide form provides maximum magnesium per capsule Evidence A-grade Per dose

Laxative effects for constipation

Effective for treating occasional constipation

Osmotic laxative effect draws water into intestines Evidence A-grade 6-12 hours

Basic magnesium deficiency correction

Can help correct severe magnesium deficiency over time

Provides significant magnesium despite lower absorption Evidence B-grade 4-12 weeks

Long shelf life

Very stable form with excellent storage properties

Simple oxide compound resistant to degradation Evidence A-grade Years of stability

Or a different form of the same thing

the comparison people search most

Magnesium Oxide vs Magnesium Glycinate absorption 4 against 90 · $8 against $25 a month 90% Magnesium Oxide vs Magnesium Citrate absorption 4 against 35 · $8 against $15 a month 35% Magnesium Oxide vs Magnesium Chloride absorption 4 against 50 · $8 against $20 a month 50% Magnesium Oxide vs Magnesium Malate absorption 4 against 40 · $8 against $35 a month 40% Magnesium Oxide vs Magnesium L-Threonate absorption 4 against 95 · $8 against $120 a month 95%

All Magnesium forms ranked by absorption →

Every pair we checked

12 combinations scored by the engine

Magnesium Oxide + Caffeine No documented interaction either way No known interaction 70

Magnesium Oxide + Creatine Monohydrate No documented interaction either way No known interaction 70

Magnesium Oxide + Whey Protein No documented interaction either way No known interaction 70

Magnesium Oxide + Lactase No documented interaction either way No known interaction 70

Magnesium Oxide + Bovine Collagen No documented interaction either way No known interaction 70

Magnesium Oxide + DHA No documented interaction either way No known interaction 70

Magnesium Oxide + Turmeric No documented interaction either way No known interaction 70

Magnesium Oxide + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70

Magnesium Oxide + Calcium Carbonate High calcium can interfere with magnesium absorption Needs attention 76

Magnesium Oxide + Calcium Bone Formula High calcium can interfere with magnesium absorption Needs attention 76

Magnesium Oxide + Digestive Bitters Stomach acid improves dissolution and absorption Works better together 82

Magnesium Oxide + Vitamin D3 Magnesium required for vitamin D metabolism Works better together 94

Dosage

Divided doses with meals

Daily400-800 mg

Maintenance400-600 mg daily

Therapeutic600-1200 mg daily

Laxative500-1000 mg before bed

Elemental magnesiumContains ~60% elemental magnesium

Upper limit 350 mg from supplements NIH ODS

Before you take it

VeganYes

When to expect it

First Effects6-12 hours for laxative effects, 2-4 weeks for deficiency correction

Peak Benefits8-12 weeks for comprehensive magnesium status improvement

Deficiency DevelopmentWeeks to months with inadequate intake

Toxicity OnsetRare with oral supplements, mainly diarrhea

How to measure it

$40-80

MarkerSerum magnesium or RBC magnesium

OptimalSerum: 1.7-2.2 mg/dL, RBC: 4.2-6.8 mg/dL

Deficient belowSerum: <1.7 mg/dL, RBC: <4.2 mg/dL

FrequencyEvery 6-12 months if supplementing regularly

RBC magnesium more accurate for cellular magnesium status

What people actually reported to the FDA

CAERS, 379 reports naming it as the suspect

Most reported effects

Dyspnoea 38

Diarrhoea 36

Vomiting 23

Excluded from the list above: choking (55), foreign body (27), dysphagia (22). Those are people struggling with the tablet itself, not with the compound.

Named as the suspect 379 reports of 1,000+ that mention it at all

Serious outcome 87% hospitalisation, emergency room or worse

Other Serious or Important Medical Event283

Hospitalization81

Visited Emergency Room53

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Elemental magnesium 60.3% of 40.3 g/mol

Absorption Very low 4 of 100 · little of the dose reaches the bloodstream

Measured 4% of the dose PubMed 34111673

Reaches blood daily 14.5 mg

Cost per 100 mg absorbed $1.84 vs $8/month on the label

A 500 mg capsule of Magnesium Oxide contains 302 mg of magnesium. At the measured 4% absorption that is about 12.1 mg reaching your blood. How this is calculated →

Works better with

3 documented

+

Vitamin D

Magnesium required for vitamin D metabolism

Cofactor for vitamin D converting enzymes · level A

+

Calcium

Balanced ratio important for bone health

Synergistic effects on bone mineralization · level A

+

Stomach Acid

Stomach acid improves dissolution and absorption

Converts MgO to more absorbable magnesium chloride · level A

What not to take with Magnesium Oxide

2 documented

!

Calcium Excess

High calcium can interfere with magnesium absorption

Competition for absorption pathways · moderate significance

!

Fiber Phytates

Dietary fiber and phytates can bind magnesium

Chelation reduces bioavailability · moderate significance

Medication interactions

Discuss these with a pharmacist before combining

antibiotics-tetracycline-quinolones Major

Magnesium significantly reduces antibiotic absorption

What to do: Space doses 2-4 hours apart

bisphosphonates Major

Reduces bisphosphonate absorption

What to do: Take bisphosphonate 2 hours before magnesium

digoxin Moderate

May affect digoxin absorption and heart rhythm

What to do: Monitor digoxin levels and heart rhythm

Available forms

bioavailability compared

Ranks 6 of 6 among magnesium forms. Magnesium L-Threonate absorbs better — 95%. Compare all forms →

Magnesium Oxide (Powder/Capsules) 15

Magnesium Oxide (Powder/Capsules): Lowest cost, Highest elemental Mg, Laxative effect, Long shelf life

Food sources

before you supplement

Magnesium oxide not found naturally in foods Only available as supplement or antacid · 15

Dark leafy greens (natural magnesium) 150-200mg per cup cooked · 50

Nuts and seeds (natural magnesium) 75-150mg per ounce · 45

Too little

deficiency signs

Muscle cramps and spasms
Insomnia and poor sleep quality
Anxiety and irritability
Fatigue and weakness
Heart palpitations
Headaches and migraines
Constipation

Too much

toxicity signs

Diarrhea and digestive upset (most common)
Muscle weakness
Low blood pressure
Breathing difficulties (extreme doses)
Generally safe with normal kidney function

Who benefits most

budget-conscious-consumers

Most affordable way to supplement with magnesium

400-800 mg daily (divided doses)

constipation-sufferers

Effective osmotic laxative for occasional constipation

500-1000 mg before bed

severe-magnesium-deficiency

High elemental content helps correct severe deficiencies

600-1200 mg daily (divided)

antacid-users

Traditional use for heartburn and acid indigestion

400-800 mg as needed

basic-supplementation

Simple, no-frills magnesium supplementation

400-600 mg daily

Where to buy it

compare forms first

Look for Magnesium Oxide at 400-800 mg per serving. The form that matters here is Magnesium Oxide (Powder/Capsules).

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What else affects it

Beyond other supplements

!

Fiber phytates

Dietary fiber and phytates can bind magnesium

Chelation reduces bioavailability

How it works

Simple ionic magnesium release upon dissolution in stomach acid
Osmotic laxative effect draws water into intestinal lumen
Competes with other minerals for absorption in intestines
Requires conversion to magnesium chloride in stomach for absorption
Poor bioavailability due to rapid transit and low solubility
High doses saturate absorption mechanisms

Key findings

what the evidence supports

Lower bioavailability than other forms but still effective for deficiency correction
Effective osmotic laxative for constipation relief
Most cost-effective form for basic magnesium supplementation
Requires divided doses to minimize digestive upset

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Magnesium Oxide?

Documented effects: Cost-effective supplementation; High elemental magnesium content; Laxative effects for constipation; Basic magnesium deficiency correction. Most affordable way to supplement with magnesium

How much Magnesium Oxide should you take per day?

The common daily range is 400-800 mg. By goal — maintenance: 400-600 mg daily; therapeutic: 600-1200 mg daily; laxative: 500-1000 mg before bed; elemental magnesium: Contains ~60% elemental magnesium.

When is the best time to take Magnesium Oxide?

Divided doses with meals. First effects are typically reported within 6-12 hours for laxative effects, 2-4 weeks for deficiency correction.

What are the side effects of Magnesium Oxide?

At excessive doses: Diarrhea and digestive upset (most common), Muscle weakness, Low blood pressure, Breathing difficulties (extreme doses), Generally safe with normal kidney function. Safety rating at normal doses is 7 out of 10.

What should you not take with Magnesium Oxide?

Separate it from Calcium Excess, Fiber Phytates by two to four hours. High calcium can interfere with magnesium absorption

Does Magnesium Oxide interact with medications?

Documented interactions with antibiotics-tetracycline-quinolones, bisphosphonates, digoxin. Discuss these with a pharmacist before combining.

How much Magnesium Oxide is too much?

The tolerable upper intake level is 350 mg from supplements per day for adults, per NIH ODS. Above that, the risk of adverse effects rises: Diarrhea and digestive upset (most common), Muscle weakness, Low blood pressure.

How do you know if you need Magnesium Oxide?

The marker is Serum magnesium or RBC magnesium, optimal range Serum: 1.7-2.2 mg/dL, RBC: 4.2-6.8 mg/dL. Common deficiency signs: Muscle cramps and spasms, Insomnia and poor sleep quality, Anxiety and irritability, Fatigue and weakness.