Magnesium Citrate vs Magnesium Oxide

Yes. Citrate is an organic salt the body takes up considerably better than oxide, whose elemental magnesium is largely unabsorbed and acts mainly in the gut.

The cheapest Magnesium Citrate we track is $0.06 per serving; the cheapest Magnesium Oxide is $0.03 per serving — so Magnesium Oxide costs less per dose right now (August 2026).

By weight, Magnesium Citrate is about 16% elemental magnesium (~160 mg per 1,000 mg) and Magnesium Oxide is about 60% (~600 mg per 1,000 mg). A higher elemental percentage isn't automatically better value — absorption differs by form, so weigh the "magnesium" line in the Supplement Facts panel against price and absorption, not the front-label number.

Magnesium oxide contains a high percentage of elemental magnesium by weight and is inexpensive to produce, so it appears widely on shelves and is sometimes suggested by clinicians. It's often used short-term as an antacid or laxative rather than as a daily supplement, partly because a relatively small fraction of it is absorbed. It typically has the lowest sticker price among magnesium forms. Whether it's the right choice depends on your goal, so it's worth asking a clinician whether a better-absorbed form suits your situation.

Both can relieve occasional constipation because unabsorbed magnesium draws water into the bowel, and magnesium citrate is a well-known saline laxative used for this. Magnesium oxide is also used and is often cheaper per dose, though individual responses vary. These are intended for short-term relief rather than daily use, so it's best to check with a clinician before using either regularly, particularly if you have kidney problems or take other medications.

If you're choosing a magnesium supplement, citrate is generally better absorbed than oxide, so a larger share of the dose tends to reach your system. However, the evidence that magnesium reliably prevents or relieves muscle cramps is mixed and far from conclusive, so it may not help. Citrate usually costs a little more per dose than oxide. If cramps are frequent or severe, it's worth talking to a clinician, since cramps can have causes that supplements won't address.

There's usually no particular reason to combine them, and taking two forms mainly increases your total magnesium intake, which can cause loose stools or diarrhea. Most people are better served by choosing a single form sized to their needs rather than stacking two. If you're considering combining supplements, take other medications, or have kidney problems, it's best to check with a clinician first, since the body clears excess magnesium through the kidneys.

RDAs depend on age and sex. Adult men need 400-420 mg; adult women need 310-320 mg. Pregnancy is 350-400 mg and lactation 310-360 mg. Children range from 80 mg (1-3 years) to 240 mg (9-13 years); infants have AIs of 30-75 mg. — per the NIH Office of Dietary Supplements; general information, not medical advice.

Yes. The Tolerable Upper Intake Level for supplemental magnesium is 350 mg for adults. High supplement or medication doses can cause diarrhea, nausea, and abdominal cramping. Very high doses cause toxicity: hypotension, vomiting, difficulty breathing, irregular heartbeat, and cardiac arrest; fatal hypermagnesemia has occurred. — per the NIH Office of Dietary Supplements; general information, not medical advice.