Magnesium citrate oxide

MineralMagnesiumBest with a meal

What is it

Magnesium citrate oxide is a label term for a blend of two common magnesium supplement forms, magnesium citrate and magnesium oxide. Each form has different solubility and absorption characteristics.

Evidence for 2 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Magnesium deficiency

Strong Evidence

Magnesium supplementation reliably corrects deficiency. Citrate is well absorbed for this purpose.

Constipation

Good Evidence

Magnesium citrate and oxide are commonly used as osmotic laxatives, with consistent evidence of effect.

How it works

Magnesium is essential for over 300 enzyme reactions, including those involved in muscle contraction, nerve function, blood pressure regulation, blood sugar control, and protein synthesis. The body absorbs magnesium primarily in the small intestine. Magnesium citrate is highly soluble and well absorbed. Magnesium oxide is poorly soluble and has lower absorption (about 4% bioavailability versus about 25-30% for citrate), but is dense in elemental magnesium per milligram. Blends pair the higher elemental content of oxide with the better absorption of citrate.

Dosage

The RDA for magnesium is 400-420 mg/day for adult men and 310-320 mg/day for adult women. The UL for supplemental magnesium (not from food) is 350 mg/day. Most supplements provide 200-400 mg of elemental magnesium per serving.

When and how to take it

Take with food to reduce GI upset. Splitting daily doses can improve absorption and tolerance. Some people prefer evening dosing for relaxation effects.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Magnesium citrate

A commonly recommended supplement form.

Well absorbed (about 25-30%); often used for both deficiency and constipation.

Magnesium oxide

Inexpensive and widely available.

Higher elemental magnesium content but lower absorption (about 4%).

Safety

The most common side effect at high doses is loose stools or diarrhea, especially with magnesium oxide and citrate. Magnesium toxicity (very high doses) can cause low blood pressure, muscle weakness, and cardiac effects, almost exclusively in people with impaired kidney function.

Who should be cautious

People with kidney disease should not take supplemental magnesium without medical supervision. Use caution with magnesium-containing antacids if also taking high-dose magnesium supplements.

Interactions

Magnesium reduces absorption of bisphosphonates, tetracyclines, and fluoroquinolones if taken together; separate by 2 hours. May potentiate calcium channel blockers and muscle relaxants at very high doses.

Food sources

Pumpkin seeds

Amount
1 oz
%DV
37%

Spinach, cooked

Amount
1/2 cup
%DV
19%

Almonds

Amount
1 oz
%DV
19%

Black beans

Amount
1/2 cup
%DV
14%

Frequently asked questions

Which magnesium form is best?⌄

Citrate and glycinate are well-absorbed for general supplementation. Oxide gives more elemental magnesium per pill but is less absorbed and more likely to cause diarrhea. A blend offers some of each.

Why does magnesium cause diarrhea?⌄

Unabsorbed magnesium draws water into the bowel, producing an osmotic laxative effect. This is more pronounced with magnesium oxide and citrate.

References

Magnesium citrate oxide on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Magnesium citrate oxide (PubMed search) — PubMed link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.