Calcium Magnesium Citrate

MineralCalcium-magnesium

What is it

Calcium-magnesium citrate (cal-mag citrate) is a combined mineral supplement providing both calcium and magnesium in citrate salt form. It is used for bone support, muscle function, and constipation relief.

Evidence for 3 uses

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

Bone health and osteoporosis prevention

Strong Evidence

Adequate calcium and magnesium intake are well established for bone mineralization. Supplementation benefits those with inadequate dietary intake.

Constipation (magnesium citrate)

Strong Evidence

Magnesium citrate is an effective osmotic laxative; calcium content offsets but does not eliminate this effect.

Muscle cramps

Limited Evidence

Magnesium may help some muscle cramps, especially nocturnal or pregnancy-related. Evidence is mixed.

How it works

Citrate salts of calcium and magnesium are highly bioavailable mineral forms that do not require gastric acid for absorption (unlike calcium carbonate), making them suitable for older adults and those on acid-reducing medications. Calcium supports bone mineralization, muscle contraction, nerve conduction, and blood clotting. Magnesium is required for over 300 enzymatic reactions, including those involved in energy production, muscle relaxation, and bone formation. Calcium and magnesium are physiologic counterparts: calcium drives muscle contraction, magnesium drives relaxation. The combined supplement form delivers both minerals simultaneously, which can be convenient. However, the typical 2:1 calcium-to-magnesium ratio in supplements may not match individual needs, and high-dose calcium can compete with magnesium absorption.

Dosage

Typical adult ratios: calcium 500 to 1,200 mg/day; magnesium 200 to 400 mg/day. Cal-mag citrate combinations vary. Read labels for elemental mineral content. Adult RDA: calcium 1,000 to 1,200 mg; magnesium 310 to 420 mg.

When and how to take it

Calcium absorption is best in doses under 500 mg at a time; split larger doses across meals. Magnesium citrate is generally well tolerated with or without food. Avoid taking with iron, zinc, or thyroid medications.

3 commercial forms

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

Calcium-magnesium citrate combination

Common combined supplement format.

Both citrate salts are well absorbed without gastric acid.

Calcium citrate (alone)

For those needing primarily calcium.

Better absorbed than calcium carbonate in low-acid conditions.

Magnesium citrate (alone)

For those needing primarily magnesium or for constipation.

Well absorbed; causes osmotic laxation at higher doses.

Safety

Generally well tolerated. Side effects include diarrhea (especially from magnesium citrate), gas, and bloating. Excessive calcium intake (above 2,500 mg/day) can cause kidney stones, hypercalcemia, and possibly cardiovascular concerns.

Who should be cautious

Kidney disease: consult a clinician (impaired magnesium and calcium excretion risks). History of kidney stones: avoid high calcium supplementation; magnesium citrate may be protective. Pregnancy: stick to RDA levels unless guided otherwise.

Interactions

Reduces absorption of tetracycline and quinolone antibiotics, levothyroxine, bisphosphonates, and iron supplements; separate by 2 to 4 hours. May affect blood pressure when combined with calcium channel blockers (additive on magnesium side). Compete with each other for absorption at high doses.

Food sources

Dairy (calcium)

Amount
1 cup milk
%DV
—

Leafy greens (both)

Amount
1 cup cooked
%DV
—

Nuts and seeds (magnesium)

Amount
1 oz
%DV
—

Sardines with bones (calcium)

Amount
3 oz
%DV
—

Frequently asked questions

Should I take calcium and magnesium together?⌄

Combined supplements are convenient but at high doses the minerals compete for absorption. If you need large amounts of either, consider splitting doses or separate products.

Does magnesium citrate cause diarrhea?⌄

Yes, at higher doses it functions as an osmotic laxative. Cal-mag combinations may be better tolerated than magnesium citrate alone.

References

Calcium Magnesium Citrate on Wikidata — Wikidata link

Calcium Magnesium Citrate (PubChem CID 76964450) — PubChem link

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

Research on Calcium Magnesium Citrate (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.