Quick answer

Magnesium is a mineral your muscles, nerves and bones rely on. Adults need about 310 to 420 mg a day from all sources, and magnesium from supplements should stay under 350 mg a day unless a doctor advises more. Forms that dissolve well are absorbed better than magnesium oxide.^1,2

Key facts

Magnesium is a helper for more than 300 enzyme systems in the body.²
Many Americans get less magnesium from food than they need, although food and supplements together usually reach the recommended amount.^1,2
Magnesium in food is not limited; the upper limit of 350 mg a day applies to supplements and medicines.¹
Magnesium can keep some antibiotics from being absorbed, so ask a pharmacist before combining them.^1,3

What magnesium does

Magnesium is a helper for more than 300 enzyme systems in the body.²

The body uses magnesium to make energy, build protein, and move calcium and potassium in and out of cells, which is how nerves send signals and muscles contract and relax. About half of the body's magnesium is stored in bone.²

When intake runs low, the kidneys hold on to more of it, so a short stretch of eating less magnesium produces no obvious signs.¹

What the evidence shows

Each claim below carries a grade, with the amount the studies used beside it. The sleep evidence is early, and the research does not back the muscle cramp or exercise claims often made for magnesium.^4,5

Helps you reach the recommended daily magnesium intake*²

Moderate evidence

National survey data from 2013 to 2016 show that 48% of Americans take in less magnesium from food and drink than the estimated average requirement. One serving supplies 275 mg, 65% of the Daily Value. In an earlier national survey, adults who used magnesium supplements had average total intakes well above requirement levels.

Amount studied: Recommended intake: 400 to 420 mg a day for men, 310 to 320 mg for women, from all sources

Contributes to normal muscle and nerve function*^2,4,6

Moderate evidence

A long-established role of the mineral, described by NIH and included in the EU list of permitted nutrient-function statements. It does not mean extra magnesium improves performance in people who already get enough: a meta-analysis of 14 trials found no significant gains in muscle strength or power, with benefits appearing only in groups likely to be short of magnesium, such as older adults.

Amount studied: Recommended daily intake from food and supplements

Contributes to the normal structure of bone*^1,2

Moderate evidence

A long-established role of the mineral, described by NIH: half or more of the body's magnesium is held in bone, where it is part of the bone's structure and takes part in bone formation. This is a role of the nutrient. NIH describes the trials of whether extra magnesium changes bone density as few and small, and says more research is needed.

Amount studied: Recommended daily intake from food and supplements

May modestly improve self-rated sleep in adults who sleep poorly*^7,8

Early evidence

One randomized, placebo-controlled trial tested this form: 155 adults who slept poorly took magnesium bisglycinate (250 mg of magnesium a day) or placebo for four weeks. Scores on a sleep-problem questionnaire fell a little more with magnesium (3.9 points against 2.3), a small effect, and other measures did not differ. It is a single short trial that relied on self-report. Older trials used other forms at higher doses in older adults and were rated low quality.

Amount studied: 250 mg a day as bisglycinate, 30 to 60 minutes before bed, for four weeks

As magnesium L-threonate, may modestly improve some measures of sleep and memory in adults who report poor sleep*^9,10

Early evidence

Two short placebo-controlled trials, both funded by companies that sell this form, tested it in adults who reported poor sleep. In 80 adults taking 1 g of the compound a day (about 75 mg of magnesium) for 21 days, the main sleep questionnaire improved about as much with placebo, while ring-measured deep and REM sleep scores and several daytime ratings came out better with the compound. In 100 adults taking 2 g a day (145 mg of magnesium) for six weeks, overall scores on a computer test of thinking and memory, and on one sleep questionnaire, came out better, while ring-measured sleep and most other sleep measures did not differ. No trial by researchers independent of the makers was found.

Amount studied: 1 to 2 g a day of magnesium L-threonate (about 75 to 145 mg of magnesium), for three to six weeks

How much you need

Men need 400 to 420 mg of magnesium a day from all sources.¹

Women need 310 to 320 mg a day, and 350 to 360 mg during pregnancy.¹

Magnesium for adults, per day¹
Who	Recommended, all sources	Upper limit, supplements and medicines
Men	400 to 420 mg	350 mg
Women	310 to 320 mg	350 mg
Pregnancy	350 to 360 mg	350 mg

The upper limit can look lower than the recommended amount. That is because the recommended amount counts food, and the limit counts only supplements and medicines.¹

Which form

Forms of magnesium that dissolve well in liquid, such as citrate, chloride, lactate and aspartate, are absorbed more completely than magnesium oxide.²

In the one isotope study of the glycinate form, 12 people absorbed about as much as from oxide overall, more in the four who absorbed oxide worst, and tolerated it better.¹¹

Labels list the amount of magnesium itself, not the weight of the whole compound. Compare that figure across products rather than the size of the capsule.

Food sources

Legumes, nuts, seeds, whole grains and green leafy vegetables such as spinach provide magnesium, as do fortified breakfast cereals, milk and yogurt.¹

Magnesium that is naturally present in food and drinks is not harmful and does not need to be limited; the upper limit applies to supplements and medicines only.¹

What's in ours

What’s in ours

Magnesium Glycinate: Magnesium, 275 mg per serving, from the label
Men's Multi: Magnesium, 50 mg per serving, from the label
Creatine + Electrolytes: Magnesium, 60 mg per serving, from the label

Side effects, medicines, and who should ask first

High intakes of magnesium from supplements and medicines can cause diarrhea, nausea and abdominal cramping.¹

The upper limit for magnesium from supplements and medicines is 350 mg a day for adults. It does not count magnesium in food and drinks.^1,2

Ask your pharmacist how far apart to take them

Tetracycline antibiotics such as doxycycline may not be absorbed if taken too soon before or after a product that contains magnesium. The doxycycline label says antacids containing magnesium impair the absorption of tetracyclines.^1,2,3

On the medicine's label

Ask your pharmacist how far apart to take them

Magnesium can bind quinolone antibiotics such as ciprofloxacin and levofloxacin in the gut, so less of the antibiotic is absorbed. The ciprofloxacin label lists magnesium and aluminum antacids, multivitamins and other products with minerals such as calcium, iron or zinc among those that lower its absorption.^2,12

On the medicine's label

Ask your pharmacist how far apart to take them

Supplements and medicines rich in magnesium can reduce the absorption of oral bisphosphonates such as alendronate. The alendronate label says calcium, antacids and oral medicines containing minerals such as magnesium interfere with its absorption.^1,2,13

On the medicine's label

Ask your pharmacist or doctor first

Long-term use of loop diuretics such as furosemide, and of thiazide diuretics such as hydrochlorothiazide, can increase the magnesium lost in urine, while potassium-sparing diuretics such as spironolactone reduce it. The furosemide label says it may lower blood magnesium and that levels should be checked periodically.^1,2,14

On the medicine's label

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and esomeprazole can cause low blood magnesium when taken for a long time, usually more than a year. The omeprazole label says this has been reported rarely after at least three months and that doctors may check magnesium before and during long-term use.^1,2,15

On the medicine's label

Ask your pharmacist how far apart to take them

The gabapentin label says an antacid containing magnesium and aluminum hydroxides lowered the amount of gabapentin the body absorbed by about 20%. In a small study, 1 g of magnesium oxide taken with gabapentin lowered its absorption by about a third.^16,17,18

On the medicine's label

Ask your pharmacist how far apart to take them

The levothyroxine label lists antacids, such as those made with aluminum and magnesium hydroxides, among products that may reduce levothyroxine absorption by lowering stomach acid. In a small 2025 study, magnesium aspartate taken at the same time lowered levothyroxine absorption by 12%, and magnesium citrate by 7%, a drop too small to rule out chance.^19,20,21

On the medicine's label

Ask first if you take an antibiotic, a bisphosphonate, a diuretic, a medicine for acid reflux, gabapentin or levothyroxine
Ask first if you have kidney disease or reduced kidney function
Ask first if you are pregnant or nursing

Questions people ask

Which form of magnesium is best?

Forms that dissolve well, such as citrate, chloride, lactate and aspartate, are absorbed more completely than oxide. Glycinate has little direct comparison: in its one isotope study it was absorbed about as well as oxide overall and was better tolerated.^2,11

Does magnesium help with sleep?

The evidence is early. One four-week trial of 250 mg a day as bisglycinate found a small gain in self-rated sleep, and older trials used larger amounts of other forms in older adults.^7,8

Can you take too much magnesium?

From supplements and medicines, yes. Adults should stay under 350 mg a day unless a doctor advises more, and loose stools are usually the first sign of too much. Magnesium in food does not count toward the limit.¹

See what we make

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See the Full Measure line Creatine + Electrolytes Magnesium Glycinate Men's Multi

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.